Ask every member to check the data the club stores about them

The club has to keep its member data current, and until now that meant writing
to each member by hand. "Datenüberprüfung anfragen" in the members tab sends one
mail per member, each listing that member's own record: number, name, nickname,
birth date, contact data, address, status, member since, payment frequency, and
the bank details only for members who have any.

Two decisions the record itself forced:

A field with no value is printed as "(nicht hinterlegt)" rather than left out.
The point of the mail is to have gaps filled in, and a missing line is a gap
nobody sees.

The IBAN is masked down to its country code and last four digits. That is enough
to recognise the account, and it keeps a full account number out of a mail the
club sends to dozens of people at once.

Every member is listed as a recipient, with the live memberships that have an
address preselected -- a member who resigned at year's end may still need to
confirm their address, so the board can add them by hand. Members without an
address are skipped and reported instead of failing the run.

Delivery reuses the existing mail machinery: the configured delivery mode, one
SMTP/IMAP connection for the whole run, an archive copy in the member file, a
"data_review_email_sent" event, and the read-only guard before anything is
rendered. A member whose mail fails is reported as a warning and the run
continues -- one bad address must not stop a mailing to the whole club halfway
through. Because the run cannot be taken back, the recipient count is confirmed
once more before it starts.

Subject and text come from a new "Datenüberprüfung" template, editable like the
others, with {{data.sheet}} for the whole record and a {{#data}} block for a
layout of the board's own.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ccma/assets/CHANGELOG.json

@@ -41,7 +41,8 @@
       "Direkt versandte Mahnungen und SEPA-Info-Mails können zusätzlich automatisch in einen Gesendet-Ordner des Postfachs abgelegt werden. Für den Entwürfe- und den Gesendet-Ordner lässt sich die tatsächliche Ordnerliste live vom Server abrufen und per Dropdown auswählen; ein noch nicht vorhandener, frei eingegebener Ordner wird bei Bedarf automatisch angelegt.",
       "Die Texte aller erzeugten E-Mails (Willkommen, Mahnung, SEPA-Vorabinformation) stecken jetzt in bearbeitbaren Vorlagen: Sie werden als Standard mitgeliefert, landen beim ersten Start im Mitglieder-Store unter templates/mail/ und können unter Optionen → E-Mail-Vorlagen mit Betreff, Text und Platzhaltern angepasst oder auf den Standardtext zurückgesetzt werden.",
       "Für neue Mitglieder kann direkt aus der Mitgliederakte eine Willkommens- und Erstrechnungsmail erzeugt werden: Sie begrüßt das Mitglied, nennt Mitgliedsnummer und Beginn der Mitgliedschaft und stellt die noch offenen Forderungen (Aufnahmegebühr und erster Beitrag) mit Zahlungshinweis zusammen; einzelne Forderungen lassen sich abwählen und die fertige Mail vorab ansehen.",
-      "CCMA startet jetzt auch, wenn der Mitglieder-Store schreibgeschützt eingebunden ist (z. B. ein nur lesend gemountetes Crypt-Laufwerk): Die Daten lassen sich wie gewohnt ansehen, der Hausmeister wird übersprungen und alle schreibenden Aktionen werden mit einer verständlichen Meldung abgelehnt statt mit einem Systemfehler. Ein dauerhaft sichtbarer Warnhinweis über den Tabs sowie Markierungen in Fenstertitel und Statusleiste weisen auf den Nur-Lese-Betrieb hin; wird der Store wieder mit Schreibrechten eingebunden, genügt „Erneut prüfen“ ohne Neustart."
+      "CCMA startet jetzt auch, wenn der Mitglieder-Store schreibgeschützt eingebunden ist (z. B. ein nur lesend gemountetes Crypt-Laufwerk): Die Daten lassen sich wie gewohnt ansehen, der Hausmeister wird übersprungen und alle schreibenden Aktionen werden mit einer verständlichen Meldung abgelehnt statt mit einem Systemfehler. Ein dauerhaft sichtbarer Warnhinweis über den Tabs sowie Markierungen in Fenstertitel und Statusleiste weisen auf den Nur-Lese-Betrieb hin; wird der Store wieder mit Schreibrechten eingebunden, genügt „Erneut prüfen“ ohne Neustart.",
+      "Über „Datenüberprüfung anfragen“ in der Mitgliederliste kann eine Bitte um Datenprüfung an beliebig viele Mitglieder auf einmal verschickt werden: Jede Mail listet den eigenen Datensatz des Empfängers auf (fehlende Angaben werden als solche ausgewiesen, die IBAN nur mit den letzten vier Stellen), vorausgewählt sind alle laufenden Mitgliedschaften mit E-Mail-Adresse. Text und Betreff stammen aus der neuen Vorlage „Datenüberprüfung“; jede Mail wird in der Mitgliederakte archiviert und in der Chronik vermerkt."
     ]
   },
   {

src/ccma/assets/mail_templates/datenpruefung.txt

@@ -0,0 +1,14 @@
+Betreff: Bitte prüfen: deine bei {{organization.name}} gespeicherten Daten
+
+Liebes Mitglied,
+
+folgende Daten haben wir über dich gespeichert. Wir bitten dich, diese einmal zu überprüfen und uns Änderungen ggf. mitzuteilen.
+
+{{data.sheet}}
+
+Deine IBAN zeigen wir hier absichtlich nur verkürzt an – die letzten vier Stellen genügen zum Abgleich.
+
+Stimmt etwas nicht oder fehlt eine Angabe? Dann antworte einfach auf diese Mail oder schreib uns an {{organization.email}}, dann pflegen wir die Änderung ein. Wenn alles passt, musst du nichts weiter tun.
+
+Viele Grüße
+{{signature}}

src/ccma/domain/mail_templates.py

@@ -97,6 +97,21 @@ BASE_PLACEHOLDERS: tuple[tuple[str, str], ...] = (
     ("signature", "Signatur aus dem Versandfenster"),
 )
 
+# The fields a member can check but which no other mail needs, so they stay out of
+# BASE_PLACEHOLDERS: the data-review mail is the one that prints the whole record.
+MEMBER_RECORD_PLACEHOLDERS: tuple[tuple[str, str], ...] = (
+    ("member.birth_date", "Geburtsdatum"),
+    ("member.phone", "Telefonnummer"),
+    ("member.street", "Straße und Hausnummer"),
+    ("member.address_addition", "Adresszusatz"),
+    ("member.postal_code", "Postleitzahl"),
+    ("member.city", "Ort"),
+    ("member.country", "Land"),
+    ("member.account_holder", "Kontoinhaber"),
+    ("member.iban_masked", "IBAN, bis auf die letzten vier Stellen maskiert"),
+    ("member.mandate_signed_at", "Datum der Mandatserteilung"),
+)
+
 CLAIM_ITEM_PLACEHOLDERS: tuple[tuple[str, str], ...] = (
     ("claim.title", "Bezeichnung der Forderung"),
     ("claim.description", "Beschreibung inkl. abgerechnetem Zeitraum"),
@@ -186,6 +201,33 @@ MAIL_TEMPLATES: tuple[MailTemplateSpec, ...] = (
             ("debit.mandate_reference", "Mandatsreferenz"),
         ),
     ),
+    MailTemplateSpec(
+        key="data_review",
+        label="Datenüberprüfung",
+        filename="datenpruefung.txt",
+        description=(
+            "Bitte an ein Mitglied, die über es gespeicherten Daten zu prüfen. Wird an "
+            "beliebig viele Mitglieder auf einmal verschickt und listet je Empfänger "
+            "dessen eigenen Datensatz auf."
+        ),
+        placeholders=BASE_PLACEHOLDERS
+        + MEMBER_RECORD_PLACEHOLDERS
+        + (
+            ("data.sheet", "Alle gespeicherten Daten als Liste, eine Zeile je Feld"),
+            ("data.count", "Anzahl der aufgeführten Felder"),
+        ),
+        blocks=(
+            MailTemplateBlock(
+                name="data",
+                description="Wiederholt sich je gespeichertem Datenfeld",
+                placeholders=(
+                    ("field.label", "Bezeichnung des Feldes"),
+                    ("field.value", "Gespeicherter Wert"),
+                ),
+                sample="{{field.label}}: {{field.value}}",
+            ),
+        ),
+    ),
 )
 
 

src/ccma/services/member_data_mail.py

@@ -0,0 +1,316 @@
+from __future__ import annotations
+
+import hashlib
+import re
+from contextlib import nullcontext
+from dataclasses import dataclass
+from datetime import date, datetime
+from pathlib import Path
+
+from ccma.domain.dates import format_date_for_display
+from ccma.domain.models import (
+    MEMBERSHIP_STATUS_LABELS,
+    PAYMENT_FREQUENCY_LABELS,
+    Member,
+)
+from ccma.services.mail_composition import compose_mail, render_template, template_values
+from ccma.services.mail_delivery import (
+    append_message,
+    ensure_imap_folder,
+    imap_session,
+    send_via_smtp,
+    smtp_session,
+)
+from ccma.storage.repository import MemberRepository, RepositoryError
+
+# Everyone the club still has a live relationship with. An ended membership is not
+# asked to check data the club is about to delete anyway, and an application has not
+# been decided on yet -- both can still be picked by hand in the dialog.
+DEFAULT_RECIPIENT_STATUSES: tuple[str, ...] = (
+    "accepted_pending_payment",
+    "active",
+    "suspended_contribution",
+    "resigned_end_of_year",
+    "honorary",
+)
+
+# A field the member is meant to complete reads better as a visible gap than as an
+# empty line the eye skips over.
+NOT_STORED = "(nicht hinterlegt)"
+
+
+@dataclass(frozen=True, slots=True)
+class GeneratedDataReviewMail:
+    member_id: str
+    recipient: str
+    # None for "send"/"drafts" delivery -- see reminder_mail.GeneratedReminderMail.
+    export_path: Path | None
+    archive_path: Path
+
+
+def _safe_filename(value: str) -> str:
+    cleaned = re.sub(r"[^A-Za-z0-9._-]+", "-", value.strip()).strip("-._")
+    return cleaned or "Mitglied"
+
+
+def _available_path(directory: Path, filename: str) -> Path:
+    candidate = directory / filename
+    if not candidate.exists():
+        return candidate
+    stem, suffix = Path(filename).stem, Path(filename).suffix
+    index = 2
+    while (directory / f"{stem}-{index}{suffix}").exists():
+        index += 1
+    return directory / f"{stem}-{index}{suffix}"
+
+
+def mask_iban(iban: str) -> str:
+    """Shows enough of the IBAN to recognise the account (country code and the last
+    four digits) without putting the full account number into an e-mail: the member
+    only has to confirm it is still the right account."""
+    cleaned = iban.replace(" ", "").strip()
+    if len(cleaned) < 8:
+        return cleaned
+    return f"{cleaned[:2]}{'*' * (len(cleaned) - 6)}{cleaned[-4:]}"
+
+
+def member_data_fields(member: Member) -> list[tuple[str, str]]:
+    """The stored record as the member gets to see it: label and value, in the order
+    they read naturally. Bank details are only listed for members who have any --
+    asking someone who pays by transfer to check a mandate they never gave is noise."""
+    fields: list[tuple[str, str]] = [
+        ("Mitgliedsnummer", member.member_number),
+        ("Name", " ".join(part for part in (member.first_name, member.last_name) if part)),
+        ("Nickname", member.nickname),
+        ("Geburtsdatum", format_date_for_display(member.birth_date)),
+        ("E-Mail", member.email),
+        ("Telefon", member.phone),
+        ("Straße und Hausnummer", member.street),
+    ]
+    if member.address_addition.strip():
+        fields.append(("Adresszusatz", member.address_addition))
+    fields.extend(
+        [
+            (
+                "PLZ und Ort",
+                " ".join(part for part in (member.postal_code, member.city) if part),
+            ),
+            ("Land", member.country),
+            ("Mitgliedsstatus", MEMBERSHIP_STATUS_LABELS.get(member.status, member.status)),
+            ("Mitglied seit", format_date_for_display(member.membership_started_at)),
+            (
+                "Zahlweise",
+                PAYMENT_FREQUENCY_LABELS.get(
+                    member.payment_frequency, member.payment_frequency
+                ).capitalize(),
+            ),
+        ]
+    )
+    if any(
+        value.strip() for value in (member.iban, member.mandate_reference, member.account_holder)
+    ):
+        signed = format_date_for_display(member.mandate_signed_at)
+        fields.extend(
+            [
+                ("Kontoinhaber", member.account_holder),
+                ("IBAN", mask_iban(member.iban)),
+                ("Mandatsreferenz", member.mandate_reference),
+                (
+                    "Lastschriftmandat",
+                    ("aktiv" if member.mandate_active else "nicht aktiv")
+                    + (f", erteilt am {signed}" if signed else ""),
+                ),
+            ]
+        )
+    return [(label, value.strip() or NOT_STORED) for label, value in fields]
+
+
+def data_review_recipients(
+    repository: MemberRepository, *, statuses: tuple[str, ...] | None = None
+) -> list[Member]:
+    """The members a data-review run is meant for by default -- an e-mail address is
+    required, so members without one are left out here and reported by the dialog."""
+    wanted = set(statuses if statuses is not None else DEFAULT_RECIPIENT_STATUSES)
+    return [
+        member
+        for member in repository.list_members()
+        if member.status in wanted and member.email.strip()
+    ]
+
+
+def data_review_mail_bytes(
+    repository: MemberRepository,
+    *,
+    member: Member,
+    organization: dict,
+    sender_name: str,
+    sender_email: str,
+    signature: str,
+    created_at: datetime | None = None,
+) -> bytes:
+    values = template_values(member, organization, signature=signature, created_at=created_at)
+    fields = member_data_fields(member)
+    entries = [{"field.label": label, "field.value": value} for label, value in fields]
+    values.update(
+        {
+            "member.iban_masked": mask_iban(member.iban),
+            "data.sheet": "\n".join(f"{label}: {value}" for label, value in fields),
+            "data.count": str(len(fields)),
+        }
+    )
+    rendered = render_template(repository, "data_review", values, {"data": entries})
+    return compose_mail(
+        recipient=member.email,
+        subject=rendered.subject,
+        body=rendered.body,
+        sender_name=sender_name,
+        sender_email=sender_email,
+        created_at=created_at,
+    )
+
+
+def generate_data_review_mails(
+    repository: MemberRepository,
+    member_ids: list[str],
+    *,
+    delivery_mode: str,
+    output_directory: Path | str | None = None,
+    sender_name: str,
+    sender_email: str,
+    signature: str,
+    today: date | None = None,
+) -> tuple[list[GeneratedDataReviewMail], list[str]]:
+    """Sends one data-review mail per member. A member whose mail fails is reported as
+    a warning and the run continues: a single bad address must not stop a mailing to
+    the whole club halfway through."""
+    repository.assert_writable()
+    output: Path | None = None
+    email_settings: dict | None = None
+    smtp_ctx = nullcontext(None)
+    imap_ctx = nullcontext(None)
+    if delivery_mode == "local":
+        if not output_directory:
+            raise RepositoryError("Kein Zielordner für die lokale Ablage angegeben.")
+        output = Path(output_directory)
+        output.mkdir(parents=True, exist_ok=True)
+    elif delivery_mode == "send":
+        email_settings = repository.get_email_settings()
+        smtp_ctx = smtp_session(email_settings)
+        if email_settings["imap_sent_enabled"]:
+            imap_ctx = imap_session(email_settings)
+    elif delivery_mode == "drafts":
+        email_settings = repository.get_email_settings()
+        imap_ctx = imap_session(email_settings)
+    else:
+        raise RepositoryError(f"Unbekannter Versandmodus: {delivery_mode}")
+
+    organization = repository.get_configuration().get("organization") or {}
+    stamp = (today or date.today()).isoformat()
+    generated: list[GeneratedDataReviewMail] = []
+    warnings: list[str] = []
+    # One connection for the whole run -- this mailing covers every member, so
+    # reconnecting per recipient would be slow and invites provider rate limits.
+    with smtp_ctx as smtp_client, imap_ctx as imap_client:
+        if delivery_mode == "drafts":
+            ensure_imap_folder(imap_client, email_settings["imap_drafts_folder"])
+        elif delivery_mode == "send" and imap_client is not None:
+            ensure_imap_folder(imap_client, email_settings["imap_sent_folder"])
+        for member_id in member_ids:
+            try:
+                member = repository.get_member(member_id)
+            except RepositoryError as exc:
+                warnings.append(f"{member_id}: {exc}")
+                continue
+            label = member.member_number or member.display_name
+            if not member.email.strip():
+                warnings.append(f"{label}: E-Mail-Adresse fehlt.")
+                continue
+            export_path: Path | None = None
+            archive_path: Path | None = None
+            # Once this mail has left the building, a later archiving failure must not
+            # hide that it went out, nor abort the members that come after it.
+            delivered = False
+            archive_failure: Exception | None = None
+            try:
+                content = data_review_mail_bytes(
+                    repository,
+                    member=member,
+                    organization=organization,
+                    sender_name=sender_name,
+                    sender_email=sender_email,
+                    signature=signature,
+                )
+                filename = f"Datenpruefung-{stamp}-{_safe_filename(label)}.eml"
+                archive_dir = (
+                    repository.members_root
+                    / member.member_id
+                    / "files"
+                    / "documents"
+                    / "Datenpruefung"
+                )
+                archive_dir.mkdir(parents=True, exist_ok=True)
+                archive_path = _available_path(archive_dir, filename)
+                if delivery_mode == "local":
+                    export_path = _available_path(output, filename)
+                    export_path.write_bytes(content)
+                    delivered = True
+                elif delivery_mode == "send":
+                    send_via_smtp(smtp_client, content)
+                    delivered = True
+                    if imap_client is not None:
+                        append_message(
+                            imap_client,
+                            content,
+                            folder=email_settings["imap_sent_folder"],
+                            flags=r"(\Seen)",
+                        )
+                else:
+                    append_message(
+                        imap_client,
+                        content,
+                        folder=email_settings["imap_drafts_folder"],
+                        flags=r"(\Draft)",
+                    )
+                    delivered = True
+                archive_path.write_bytes(content)
+            except (OSError, RepositoryError) as exc:
+                if not delivered:
+                    if export_path is not None:
+                        export_path.unlink(missing_ok=True)
+                    warnings.append(f"{label}: {exc}")
+                    continue
+                warnings.append(
+                    f"{label}: E-Mail wurde versandt/abgelegt, konnte aber nicht archiviert "
+                    f"werden ({exc}); bitte manuell prüfen."
+                )
+                archive_failure = exc
+
+            digest = hashlib.sha256(content).hexdigest()
+            references: dict[str, str] = {}
+            if archive_failure is None:
+                references["document"] = archive_path.relative_to(
+                    repository.members_root / member.member_id / "files"
+                ).as_posix()
+            data = {
+                "sha256": digest,
+                "recipient": member.email,
+                "delivery_mode": delivery_mode,
+                "field_count": len(member_data_fields(member)),
+            }
+            if archive_failure is not None:
+                data["archive_error"] = str(archive_failure)
+            repository.append_event(
+                member.member_id,
+                event_type="data_review_email_sent",
+                summary="Bitte um Datenüberprüfung verschickt",
+                actor_type="user",
+                actor_name="Vorstand",
+                references=references,
+                data=data,
+            )
+            generated.append(
+                GeneratedDataReviewMail(
+                    member.member_id, member.email, export_path, archive_path
+                )
+            )
+    return generated, warnings

src/ccma/ui/data_review_mail_dialog.py

@@ -0,0 +1,278 @@
+from __future__ import annotations
+
+import tkinter as tk
+from collections.abc import Callable
+from email.parser import BytesParser
+from email.policy import default as default_policy
+from tkinter import filedialog, messagebox, ttk
+
+from ccma.domain.models import MEMBERSHIP_STATUS_LABELS, Member
+from ccma.services.member_data_mail import (
+    data_review_mail_bytes,
+    data_review_recipients,
+    generate_data_review_mails,
+)
+from ccma.storage.repository import MemberRepository, RepositoryError
+from ccma.ui.email_delivery_dialog import resolve_delivery_mode
+
+
+class DataReviewMailDialog(tk.Toplevel):
+    """Asks the members to check the data the club stores about them. Unlike the
+    other mails this one goes out to everybody at once, so the recipients are picked
+    from a list every member appears in -- with the active ones preselected."""
+
+    def __init__(
+        self,
+        master: tk.Misc,
+        repository: MemberRepository,
+        on_sent: Callable[[], None] | None = None,
+    ):
+        super().__init__(master)
+        self.repository = repository
+        self.on_sent = on_sent
+        self.members: list[Member] = []
+        organization = repository.get_configuration().get("organization") or {}
+        self.sender_name_var = tk.StringVar(value=str(organization.get("name") or "Verwaltung C3MA"))
+        self.sender_email_var = tk.StringVar(value=str(organization.get("email") or ""))
+        self.summary_var = tk.StringVar()
+        self.warning_var = tk.StringVar()
+        self.title("Datenüberprüfung anfragen")
+        self.transient(master.winfo_toplevel())
+        self.geometry("940x620")
+        self.minsize(760, 480)
+        self._build_ui()
+        self._refresh_members()
+        self.after_idle(self.grab_set)
+
+    def _build_ui(self) -> None:
+        self.columnconfigure(0, weight=1)
+        self.rowconfigure(3, weight=1)
+        ttk.Label(
+            self,
+            text=(
+                "Bittet die ausgewählten Mitglieder, die über sie gespeicherten Daten zu "
+                "prüfen. Jede Mail listet den Datensatz genau eines Mitglieds auf; die IBAN "
+                "erscheint dabei nur mit den letzten vier Stellen. Betreff und Text stammen "
+                "aus der Vorlage unter Optionen → E-Mail-Vorlagen."
+            ),
+            wraplength=880,
+        ).grid(row=0, column=0, sticky="w", padx=14, pady=(14, 8))
+        ttk.Label(
+            self,
+            text=(
+                "Vorausgewählt sind alle aktiven Mitgliedschaften mit E-Mail-Adresse – "
+                "einzelne mit Strg+Klick ab- oder zusätzlich auswählen."
+            ),
+            style="Muted.TLabel",
+            wraplength=880,
+        ).grid(row=1, column=0, sticky="w", padx=14, pady=(0, 8))
+        ttk.Label(self, textvariable=self.summary_var, style="Mono.TLabel").grid(
+            row=2, column=0, sticky="w", padx=14, pady=(0, 6)
+        )
+        table = ttk.Frame(self)
+        table.grid(row=3, column=0, sticky="nsew", padx=14)
+        table.columnconfigure(0, weight=1)
+        table.rowconfigure(0, weight=1)
+        self.table = ttk.Treeview(
+            table,
+            columns=("number", "name", "status", "email"),
+            show="headings",
+            selectmode="extended",
+        )
+        for key, title, width, stretch in (
+            ("number", "Nummer", 90, False),
+            ("name", "Name", 220, True),
+            ("status", "Status", 200, False),
+            ("email", "E-Mail", 260, True),
+        ):
+            self.table.heading(key, text=title)
+            self.table.column(key, width=width, anchor="w", stretch=stretch)
+        self.table.grid(row=0, column=0, sticky="nsew")
+        scroll = ttk.Scrollbar(table, orient="vertical", command=self.table.yview)
+        scroll.grid(row=0, column=1, sticky="ns")
+        self.table.configure(yscrollcommand=scroll.set)
+        self.table.bind("<<TreeviewSelect>>", lambda _event: self._update_summary())
+
+        fields = ttk.Frame(self)
+        fields.grid(row=4, column=0, sticky="ew", padx=14, pady=(10, 0))
+        fields.columnconfigure(1, weight=1)
+        ttk.Label(fields, text="Absendername").grid(row=0, column=0, sticky="w", pady=5, padx=(0, 12))
+        ttk.Entry(fields, textvariable=self.sender_name_var, width=52).grid(row=0, column=1, sticky="ew")
+        ttk.Label(fields, text="Absenderadresse").grid(row=1, column=0, sticky="w", pady=5, padx=(0, 12))
+        ttk.Entry(fields, textvariable=self.sender_email_var).grid(row=1, column=1, sticky="ew")
+        ttk.Label(fields, text="Signatur").grid(row=2, column=0, sticky="nw", pady=5, padx=(0, 12))
+        self.signature = tk.Text(fields, width=52, height=4, wrap="word")
+        self.signature.grid(row=2, column=1, sticky="ew", pady=5)
+        self.signature.insert("1.0", "Der Vorstand\nChaos Computer Club Mannheim e.V.")
+
+        footer = ttk.Frame(self, padding=14)
+        footer.grid(row=5, column=0, sticky="ew")
+        footer.columnconfigure(0, weight=1)
+        ttk.Label(footer, textvariable=self.warning_var, style="Muted.TLabel", wraplength=520).grid(
+            row=0, column=0, sticky="w"
+        )
+        ttk.Button(footer, text="Abbrechen", command=self.destroy).grid(row=0, column=1, padx=(8, 0))
+        ttk.Button(footer, text="Vorschau", command=self._preview).grid(row=0, column=2, padx=(8, 0))
+        ttk.Button(
+            footer, text="Mails erzeugen", style="Accent.TButton", command=self._generate
+        ).grid(row=0, column=3, padx=(8, 0))
+
+    def _refresh_members(self) -> None:
+        try:
+            self.members = self.repository.list_members()
+            preselected = {
+                member.member_id for member in data_review_recipients(self.repository)
+            }
+        except RepositoryError as exc:
+            messagebox.showerror("Mitglieder konnten nicht gelesen werden", str(exc), parent=self)
+            return
+        self.table.delete(*self.table.get_children())
+        for index, member in enumerate(self.members):
+            self.table.insert(
+                "",
+                "end",
+                iid=str(index),
+                values=(
+                    member.member_number,
+                    member.display_name,
+                    MEMBERSHIP_STATUS_LABELS.get(member.status, member.status),
+                    member.email or "—",
+                ),
+            )
+        self.table.selection_set(
+            [
+                str(index)
+                for index, member in enumerate(self.members)
+                if member.member_id in preselected
+            ]
+        )
+        without_email = [member for member in self.members if not member.email.strip()]
+        self.warning_var.set(
+            f"{len(without_email)} Mitglied(er) ohne E-Mail-Adresse werden übersprungen."
+            if without_email
+            else ""
+        )
+        self._update_summary()
+
+    def _selected_members(self) -> list[Member]:
+        return [self.members[int(iid)] for iid in sorted(self.table.selection(), key=int)]
+
+    def _update_summary(self) -> None:
+        selected = self._selected_members()
+        reachable = [member for member in selected if member.email.strip()]
+        self.summary_var.set(
+            f"{len(selected)} von {len(self.members)} Mitgliedern ausgewählt – "
+            f"{len(reachable)} Mail(s) werden erzeugt"
+        )
+
+    def _preview(self) -> None:
+        selected = self._selected_members()
+        member = next((item for item in selected if item.email.strip()), None)
+        if member is None:
+            messagebox.showinfo(
+                "Keine Vorschau möglich",
+                "Bitte mindestens ein Mitglied mit E-Mail-Adresse auswählen.",
+                parent=self,
+            )
+            return
+        try:
+            content = data_review_mail_bytes(
+                self.repository,
+                member=member,
+                organization=self.repository.get_configuration().get("organization") or {},
+                sender_name=self.sender_name_var.get(),
+                sender_email=self.sender_email_var.get(),
+                signature=self.signature.get("1.0", "end-1c"),
+            )
+        except (OSError, RepositoryError) as exc:
+            messagebox.showerror("Vorschau nicht möglich", str(exc), parent=self)
+            return
+        message = BytesParser(policy=default_policy).parsebytes(content)
+        window = tk.Toplevel(self)
+        window.title(f"Vorschau für {member.display_name}")
+        window.transient(self)
+        window.columnconfigure(0, weight=1)
+        window.rowconfigure(1, weight=1)
+        ttk.Label(window, text=f"Betreff: {message['Subject']}", padding=12).grid(
+            row=0, column=0, sticky="w"
+        )
+        preview = tk.Text(window, wrap="word", width=88, height=30)
+        preview.grid(row=1, column=0, sticky="nsew", padx=12, pady=(0, 12))
+        preview.insert("1.0", message.get_content())
+        preview.configure(state="disabled")
+        scroll = ttk.Scrollbar(window, orient="vertical", command=preview.yview)
+        scroll.grid(row=1, column=1, sticky="ns", pady=(0, 12), padx=(0, 12))
+        preview.configure(yscrollcommand=scroll.set)
+        ttk.Button(window, text="Schließen", command=window.destroy).grid(
+            row=2, column=0, columnspan=2, sticky="e", padx=12, pady=(0, 12)
+        )
+
+    def _generate(self) -> None:
+        recipients = [member for member in self._selected_members() if member.email.strip()]
+        if not recipients:
+            messagebox.showinfo(
+                "Keine Empfänger",
+                "Bitte mindestens ein Mitglied mit E-Mail-Adresse auswählen.",
+                parent=self,
+            )
+            return
+        delivery_mode = resolve_delivery_mode(self, self.repository)
+        if delivery_mode is None:
+            return
+        output_directory = None
+        if delivery_mode == "local":
+            selected = filedialog.askdirectory(
+                parent=self,
+                title="Ausgabeordner für die Thunderbird-Entwürfe auswählen",
+                mustexist=True,
+            )
+            if not selected:
+                return
+            output_directory = selected
+        # A mailing to the whole club cannot be taken back, so the count is confirmed
+        # once more -- especially when "Senden" would put it on the wire right away.
+        action = {
+            "local": "als Datei abgelegt",
+            "send": "sofort versandt",
+            "drafts": "als Entwurf im Postfach abgelegt",
+        }[delivery_mode]
+        if not messagebox.askyesno(
+            "Datenüberprüfung verschicken",
+            f"An {len(recipients)} Mitglied(er) wird je eine Mail mit deren gespeicherten "
+            f"Daten {action}.\n\nJetzt erzeugen?",
+            parent=self,
+        ):
+            return
+        self.configure(cursor="watch")
+        self.update_idletasks()
+        try:
+            generated, warnings = generate_data_review_mails(
+                self.repository,
+                [member.member_id for member in recipients],
+                delivery_mode=delivery_mode,
+                output_directory=output_directory,
+                sender_name=self.sender_name_var.get(),
+                sender_email=self.sender_email_var.get(),
+                signature=self.signature.get("1.0", "end-1c"),
+            )
+        except (OSError, RepositoryError) as exc:
+            messagebox.showerror("Mails konnten nicht erzeugt werden", str(exc), parent=self)
+            return
+        finally:
+            self.configure(cursor="")
+        location = {
+            "local": f"in\n{output_directory}\nerzeugt",
+            "send": "versandt",
+            "drafts": "als Entwurf im Postfach abgelegt",
+        }[delivery_mode]
+        detail = (
+            f"{len(generated)} Mail(s) wurden {location} und in den Mitgliederakten archiviert."
+        )
+        if warnings:
+            detail += "\n\nÜbersprungen:\n" + "\n".join(warnings[:12])
+            if len(warnings) > 12:
+                detail += f"\n… und {len(warnings) - 12} weitere."
+        messagebox.showinfo("Datenüberprüfung verschickt", detail, parent=self)
+        self.destroy()
+        if self.on_sent is not None:
+            self.on_sent()

src/ccma/ui/main_window.py

@@ -10,6 +10,7 @@ from ccma.services.housekeeper import Housekeeper
 from ccma.storage.repository import MemberRepository, RepositoryError
 from ccma.ui.asset_tab import AssetTab
 from ccma.ui.claim_tab import ClaimTab
+from ccma.ui.data_review_mail_dialog import DataReviewMailDialog
 from ccma.ui.dialogs import EditAssetDialog, IssueAssetDialog, NewAssetDialog, NewMemberDialog
 from ccma.ui.icons import IconStore
 from ccma.ui.member_tab import MemberTab
@@ -445,6 +446,7 @@ class MainWindow(ttk.Frame):
             self.findings,
             self.open_member,
             lambda: self.tabs.close(key),
+            self.open_data_review_mail,
         )
         self.tabs.add(
             key,
@@ -480,6 +482,11 @@ class MainWindow(ttk.Frame):
     def open_sepa_export(self) -> None:
         SepaExportDialog(self, self.repository)
 
+    def open_data_review_mail(self) -> None:
+        if self._refuse_read_only("Der Versand der Datenüberprüfung"):
+            return
+        DataReviewMailDialog(self, self.repository)
+
     def new_member(self) -> None:
         if self._refuse_read_only("Das Anlegen eines Mitglieds"):
             return

src/ccma/ui/work_tabs.py

@@ -245,12 +245,14 @@ class MembersTab(ttk.Frame):
         findings: list[HousekeeperFinding],
         on_open: Callable[[str], None],
         on_close: Callable[[], None],
+        on_data_review: Callable[[], None] | None = None,
     ):
         super().__init__(master, padding=12)
         self.members = members
         self.findings = findings
         self.on_open = on_open
         self.on_close = on_close
+        self.on_data_review = on_data_review
         self._build_ui()
 
     def _build_ui(self) -> None:
@@ -262,7 +264,15 @@ class MembersTab(ttk.Frame):
         ttk.Label(header, text="MITGLIEDER", style="TabTitle.TLabel").grid(row=0, column=0, sticky="w")
         self.count_var = tk.StringVar()
         ttk.Label(header, textvariable=self.count_var, style="Mono.TLabel").grid(row=1, column=0, sticky="w")
-        ttk.Button(header, text="Tab schließen", command=self.on_close).grid(row=0, column=1, rowspan=2)
+        buttons = ttk.Frame(header)
+        buttons.grid(row=0, column=1, rowspan=2, sticky="e")
+        if self.on_data_review is not None:
+            # The mailing goes to every member, so it belongs where every member is
+            # listed rather than into the already crowded ribbon.
+            ttk.Button(
+                buttons, text="Datenüberprüfung anfragen", command=self.on_data_review
+            ).pack(side="left", padx=(0, 8))
+        ttk.Button(buttons, text="Tab schließen", command=self.on_close).pack(side="left")
         filters = _filter_label_frame(self)
         filters.grid(row=1, column=0, sticky="ew", pady=(0, 10))
         filter_row = ttk.Frame(filters)