fix: stop mail loops from bounces and autoresponders

[aerodeval]

What

Inbound mail is only screened with the X-Auto-Generated header, which nothing but helpdesk's own acknowledgement emails set. Real bounces and out-of-office replies pass straight through into ticket creation, where they can start a mail loop with the sending MTA.

Once a machine-generated mail becomes a ticket or a communication, three separate paths can reply to it:

1. New ticket ack — HD Ticket.after_insert sends the acknowledgement to raised_by, i.e. the address that just bounced.
2. Portal ticket threading — when the mail threads onto a ticket created from the portal, frappe CCs the parent doc's owner (mail_cc) on every inbound mail — the same dead address.
3. enable_auto_reply — an account with auto-reply on answers mailer-daemon directly.

Each reply bounces again, which creates another inbound mail, and so on.

Changes

helpdesk/overrides/email_account.py — new auto_generated_reason(msg) identifies machine-generated mail by the standard markers instead of relying on our own header:

• RFC 3834 Auto-Submitted — anything but no (parameters after the value are tolerated, e.g. no; owner=...)
• RFC 3464 multipart/report; report-type=delivery-status — catches a DSN even where no MTA added a Return-Path (POP3, Frappe Mail)
• RFC 5321 §6.1 null return-path (<>) — which bounces MUST carry
• X-Auto-Generated is kept, so our own acks are still caught

Matches now go to handle_bad_emails(uid, message, reason) and land in Unhandled Email with the reason recorded, instead of being silently dropped by a bare continue. The fetch has already marked them seen either way, so this costs nothing and leaves a trace when a real mail is misclassified.

Testing

helpdesk/overrides/test_email_account.py — 8 unit tests over auto_generated_reason with real message fixtures (Gmail DSN, out-of-office, a DSN with no Return-Path, and genuine customer replies), asserting bounces are dropped and human mail is kept, including the Auto-Submitted: no cases.

Note

These are pure stdlib email tests with no site fixtures. They currently need frappe importable, since the module imports it at the top; the function itself touches none of it.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.36170% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.93%. Comparing base (04ac2c4) to head (253623c).
⚠️ Report is 73 commits behind head on develop.

Files with missing lines	Patch %	Lines
helpdesk/overrides/email_account.py	71.42%	4 Missing ⚠️
helpdesk/overrides/test_email_account.py	96.96%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3628      +/-   ##
===========================================
+ Coverage    68.57%   68.93%   +0.36%     
===========================================
  Files          140      144       +4     
  Lines         9181     9442     +261     
===========================================
+ Hits          6296     6509     +213     
- Misses        2885     2933      +48     

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

The classifier preserves ordinary and explicitly human-submitted mail while diverting recognized automated messages through the existing per-message error-handling path.

_{Reviews (1): Last reviewed commit: "fix: stop mail loops from bounces and au..." | Re-trigger Greptile}

[aerodeval]

@RitvikSardana have to test one more thing, do not merge yet