Add "prefer SMTP" toggle to skip Microsoft Graph for email

When the M365 connector is connected the app always tries Graph first,
and a Graph 202 ends the send — so report mail to recipients Exchange
silently drops (Google-hosted subdomains of the O365 domain) never
reaches them, even with working SMTP configured.

New prefer_smtp flag gates all three Graph branches (smtp_test,
send_report, _maybe_send_auto_email) so they go straight to SMTP. UI
toggle #st-smtpPreferSmtp in Settings → E-mailrapport, saved/loaded by
scheduler.js, with da/de/en strings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

routes/CLAUDE.md

@@ -70,6 +70,7 @@ Exception hierarchy (all inherit `M365Error(Exception)`):
 - **Gmail vs Google Workspace** — auth error handlers check if SMTP username ends in `@gmail.com`/`@googlemail.com`; custom domains are treated as Google Workspace and error message points to the Workspace admin console.
 - **Canonical SMTP config keys are `username` and `use_tls`** — all backend readers (`smtp_test`, `_send_report_email`, `_send_email_graph`) use these. The Settings → E-mailrapport tab (`scheduler.js`) historically saved `user`/`starttls`, which left `username` empty so `server.login()` was skipped and the server rejected the send. Frontend now sends the canonical keys, and `_load_smtp_config()` normalises legacy `user`→`username` / `starttls`→`use_tls` for already-saved configs. The send-report modal (`scan.js`) already used the canonical keys. Keep both UIs and the backend on `username`/`use_tls`.
 - **Graph 202 ≠ delivered** — `_send_email_graph` returns on Graph's HTTP 202 (queued), and `smtp_test`/`send_report` treat that as success and never fall back to SMTP. A recipient on a domain Exchange Online considers an accepted/internal domain (e.g. a Google-hosted subdomain of the O365 domain) is silently dropped after the 202. There is no in-app fix for that routing; reaching such recipients requires SMTP (e.g. Google Workspace `smtp.gmail.com`/`smtp-relay.gmail.com`) or fixing Exchange Accepted Domains.
+- **`prefer_smtp` config flag** — when truthy, `smtp_test`, `send_report`, and `_maybe_send_auto_email` (routes/scan.py) skip the Graph path entirely and send via SMTP. This is the in-app escape hatch for the Graph-202 routing trap above. The gate is `... and not smtp_cfg.get("prefer_smtp")` on each Graph branch — keep all three in sync. UI: `#st-smtpPreferSmtp` toggle (key `m365_smtp_prefer_smtp`), saved/loaded by `scheduler.js`.
 
 ## Scheduler — scan_scheduler.py + routes/scheduler.py
 

routes/email.py

@@ -148,8 +148,12 @@ def smtp_test():
         "</body></html>"
     )
 
-    # Try Graph API first
-    if state.connector and state.connector.is_authenticated():
+    # Try Graph API first — unless the user opted to always use SMTP. Graph
+    # returns 202 (queued) even for recipients Exchange later silently drops
+    # (e.g. a Google-hosted subdomain of the O365 domain), so SMTP is the only
+    # reliable path for those; prefer_smtp forces it.
+    prefer_smtp = bool(saved.get("prefer_smtp"))
+    if state.connector and state.connector.is_authenticated() and not prefer_smtp:
         try:
             _send_email_graph(subject, body_html, recipients)
             return jsonify({"ok": True, "method": "graph", "recipients": recipients})
@@ -285,8 +289,8 @@ def send_report():
         "</body></html>"
     )
 
-    # Try Graph API first
-    if state.connector and state.connector.is_authenticated():
+    # Try Graph API first — unless prefer_smtp is set (see smtp_test for why).
+    if state.connector and state.connector.is_authenticated() and not smtp_cfg.get("prefer_smtp"):
         try:
             _send_email_graph(subject, body_html, recipients,
                               attachment_bytes=xl_bytes, attachment_name=fname)

routes/scan.py

@@ -54,7 +54,7 @@ def _maybe_send_auto_email():
             "</body></html>"
         )
 
-        if state.connector and state.connector.is_authenticated():
+        if state.connector and state.connector.is_authenticated() and not smtp_cfg.get("prefer_smtp"):
             try:
                 _send_email_graph(subject, body_html, recipients,
                                   attachment_bytes=xl_bytes, attachment_name=fname)