feat: enforce Mail-owned campaign transport boundary

src/govoplan_mail/backend/sending/imap.py

@@ -68,9 +68,16 @@ class ImapAppendError(RuntimeError):
     configuration or mailbox choice probably needs user/admin attention.
     """
 
-    def __init__(self, message: str, *, temporary: bool | None = None):
+    def __init__(
+        self,
+        message: str,
+        *,
+        temporary: bool | None = None,
+        outcome_unknown: bool = False,
+    ):
         super().__init__(message)
         self.temporary = temporary
+        self.outcome_unknown = outcome_unknown
 
 
 @dataclass(frozen=True, slots=True)
@@ -1100,10 +1107,12 @@ def append_message_to_sent(
         )
 
     client: imaplib.IMAP4 | None = None
+    append_started = False
     try:
         client = _open_imap(imap_config)
         target_folder = _effective_sent_folder(config=imap_config, requested_folder=folder, client=client)
         internal_date = imaplib.Time2Internaldate(time.time())
+        append_started = True
         typ, data = client.append(_quote_mailbox_name(target_folder), "\\Seen", internal_date, message_bytes)
         if typ != "OK":
             raise ImapAppendError(f"IMAP APPEND failed for folder {target_folder!r}: {data!r}", temporary=False)
@@ -1119,9 +1128,17 @@ def append_message_to_sent(
     except ImapAppendError:
         raise
     except (OSError, socket.timeout, imaplib.IMAP4.abort) as exc:
-        raise ImapAppendError(f"IMAP append failed: {exc}", temporary=True) from exc
+        raise ImapAppendError(
+            f"IMAP append failed: {exc}",
+            temporary=not append_started,
+            outcome_unknown=append_started,
+        ) from exc
     except imaplib.IMAP4.error as exc:
-        raise ImapAppendError(f"IMAP append failed: {exc}", temporary=False) from exc
+        raise ImapAppendError(
+            f"IMAP append failed: {exc}",
+            temporary=False,
+            outcome_unknown=append_started,
+        ) from exc
     finally:
         if client is not None:
             try: