The SECURE_REDIRECT_EXEMPT setting was missing the inbound MTA router
endpoints, causing internal HTTP calls from the MTA-in service to be
redirected to HTTPS with a 301 response.
This caused the milter to timeout when checking recipients and
delivering mail, resulting in "451 4.7.1 Service unavailable" errors.
The MTA-in service calls:
- /api/v1.0/inbound/mta/check/ (for recipient validation)
- /api/v1.0/inbound/mta/deliver/ (for mail delivery)
These internal endpoints must accept HTTP requests and should not
be redirected to HTTPS.
Changed:
- Added "^api/v1\.0/inbound/mta/" to SECURE_REDIRECT_EXEMPT
This follows the existing pattern for the alias endpoints at
/api/v1.0/mta/* which were already exempted.
Fixes: MTA milter timeout and mail delivery failures