Add authority email aliases to improve holding pen guesses

[garethrees]

Authorities sometimes use reply addresses outside their domain, which confuses the authority guessing:

Adding a further layer of guessing based on known addresses would improve the chance we find the correct authority, and reduce time taken to redeliver the message.

We could:

• Keep a list of known aliases.
• Pluck out the From addresses from previous incoming messages.

[HelenWDTK]

This issue has been automatically closed due to a lack of discussion or resolution for over 12 months.
Should we decide to revisit this issue in the future, it can be reopened.