WIP: Resolve "Emails redirected to GitLab are dropped if key is in "Received" header"

What does this MR do?

Screenshots

Backend-only change.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing

Email processing should only be slowed down when no token is found in any email headers.

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process

Security

No security impact.

Closes #199130 (closed)