Copy directly-sent e-mails to an IMAP Sent folder, with a live folder picker

A raw SMTP send has no server-side "Sent" copy on its own (unlike IMAP
drafts, which are inherently server-side) -- add an opt-in checkbox plus a
configurable target folder so directly sent Mahnungen/SEPA-info-mails still
show up in the account's Gesendet/Sent folder like a normal mail client
would leave them. Applies only to "send" delivery; drafts already live on
the server by definition.

Both the Entwürfe- and Gesendet-folder fields are now editable comboboxes:
a new "Ordnerliste laden" button fetches the real folder list from the IMAP
server (needs working credentials first) via LIST, decoding folder names
from modified UTF-7 (RFC 3501) so names like "Entwürfe" render correctly
instead of as "Entw&APw-rfe". Free text still works -- ensure_imap_folder()
creates the folder on first use if it doesn't exist yet, checked once per
batch rather than before every single message.

mail_delivery.append_to_imap_drafts() became the more general
append_message(client, content, folder=, flags=), reused for both the
\Draft and \Seen cases.

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

src/ccma/services/mail_delivery.py

@@ -1,6 +1,9 @@
 from __future__ import annotations
 
+import base64
+import binascii
 import imaplib
+import re
 import smtplib
 import ssl
 from collections.abc import Iterator
@@ -90,16 +93,127 @@ def send_via_smtp(client: smtplib.SMTP, message_bytes: bytes) -> None:
         raise RepositoryError(f"E-Mail konnte nicht versandt werden: {exc}") from exc
 
 
-def append_to_imap_drafts(client: imaplib.IMAP4, message_bytes: bytes, *, folder: str) -> None:
+def append_message(client: imaplib.IMAP4, message_bytes: bytes, *, folder: str, flags: str) -> None:
     try:
-        status, response = client.append(folder, r"(\Draft)", None, message_bytes)
+        status, response = client.append(_encode_imap_utf7(folder), flags, None, message_bytes)
     except (OSError, imaplib.IMAP4.error) as exc:
-        raise RepositoryError(f"E-Mail konnte nicht als Entwurf abgelegt werden: {exc}") from exc
+        raise RepositoryError(f"E-Mail konnte nicht in „{folder}“ abgelegt werden: {exc}") from exc
     if status != "OK":
         detail = response[0].decode("utf-8", "replace") if response and response[0] else status
         raise RepositoryError(f"IMAP-Server hat die Ablage im Ordner „{folder}“ abgelehnt: {detail}")
 
 
+def ensure_imap_folder(client: imaplib.IMAP4, folder: str) -> None:
+    """Creates the folder on the server if it doesn't exist yet -- lets someone type
+    a not-yet-existing Entwürfe/Gesendet folder name and have it just appear, instead
+    of every append failing until it's created by hand in a separate mail client."""
+    encoded = _encode_imap_utf7(folder)
+    try:
+        status, _response = client.select(encoded, readonly=True)
+    except (OSError, imaplib.IMAP4.error) as exc:
+        raise RepositoryError(f"IMAP-Ordner „{folder}“ konnte nicht geprüft werden: {exc}") from exc
+    if status == "OK":
+        return
+    try:
+        status, response = client.create(encoded)
+    except (OSError, imaplib.IMAP4.error) as exc:
+        raise RepositoryError(f"IMAP-Ordner „{folder}“ konnte nicht angelegt werden: {exc}") from exc
+    if status != "OK":
+        detail = response[0].decode("utf-8", "replace") if response and response[0] else status
+        raise RepositoryError(f"IMAP-Ordner „{folder}“ konnte nicht angelegt werden: {detail}")
+
+
+_LIST_RESPONSE_RE = re.compile(
+    rb'^\((?P<flags>[^)]*)\)\s+(?:"(?P<qdelim>[^"]*)"|(?P<delim>\S+))\s+(?P<name>.+)$'
+)
+
+
+def list_imap_folders(settings: dict) -> list[str]:
+    """Human-readable (decoded) folder names for the Options dialog's folder picker
+    -- fetched live from the server, so it only works once credentials are entered."""
+    with imap_session(settings) as client:
+        try:
+            status, response = client.list()
+        except (OSError, imaplib.IMAP4.error) as exc:
+            raise RepositoryError(f"Ordnerliste konnte nicht abgerufen werden: {exc}") from exc
+        if status != "OK":
+            raise RepositoryError("Ordnerliste konnte nicht abgerufen werden.")
+        folders = []
+        for raw in response or []:
+            if not raw:
+                continue
+            name = _parse_list_response(raw)
+            if name:
+                folders.append(name)
+        return folders
+
+
+def _parse_list_response(raw: bytes) -> str | None:
+    match = _LIST_RESPONSE_RE.match(raw)
+    if not match:
+        return None
+    name = match.group("name").decode("utf-8", "replace").strip()
+    if name.startswith('"') and name.endswith('"') and len(name) >= 2:
+        name = name[1:-1]
+    return _decode_imap_utf7(name)
+
+
+def _decode_imap_utf7(value: str) -> str:
+    # Modified UTF-7 (RFC 3501 5.1.3): "&" takes the role of "+", and "," takes the
+    # role of "/" inside the base64 run; "&-" is a literal ampersand.
+    if "&" not in value:
+        return value
+    result: list[str] = []
+    index = 0
+    length = len(value)
+    while index < length:
+        char = value[index]
+        if char != "&":
+            result.append(char)
+            index += 1
+            continue
+        end = value.find("-", index + 1)
+        if end == -1:
+            end = length
+        chunk = value[index + 1 : end]
+        if chunk == "":
+            result.append("&")
+        else:
+            base64_chunk = chunk.replace(",", "/")
+            base64_chunk += "=" * (-len(base64_chunk) % 4)
+            try:
+                result.append(base64.b64decode(base64_chunk).decode("utf-16-be"))
+            except (binascii.Error, UnicodeDecodeError):
+                result.append("&" + chunk + "-")
+        index = end + 1
+    return "".join(result)
+
+
+def _encode_imap_utf7(value: str) -> str:
+    if "&" not in value and all(32 <= ord(char) <= 126 for char in value):
+        return value
+    result: list[str] = []
+    index = 0
+    length = len(value)
+    while index < length:
+        char = value[index]
+        if char == "&":
+            result.append("&-")
+            index += 1
+            continue
+        if 32 <= ord(char) <= 126:
+            result.append(char)
+            index += 1
+            continue
+        start = index
+        while index < length and not (32 <= ord(value[index]) <= 126):
+            index += 1
+        chunk = value[start:index]
+        encoded = base64.b64encode(chunk.encode("utf-16-be")).decode("ascii").rstrip("=")
+        result.append("&" + encoded.replace("/", ",") + "-")
+    return "".join(result)
+
+
 def test_smtp_connection(settings: dict) -> None:
     with smtp_session(settings):
         pass