This PR adds functionality for the IMAP sync code to detect if a UID that is missing from the mail group mailbox is in the Spam/Junk folder for the mail account, and if so delete the associated Discourse topic. This is identical to what we do for emails that are moved for Trash.
If an email is missing but not in Spam or Trash, then we mark the incoming email record with imap_missing: true. This may be used in future to further filter or identify these emails, and perhaps go hunting for them in the email account in bulk.
Note: This adds some code duplication because the trash and spam email detection and handling is very similar. I intend to do more refactors/improvements to the IMAP sync code in time because there is a lot of room for improvement.
Previously we did an early return if either SiteSetting.tagging_enabled or SiteSetting.allow_staff_to_tag_pms was false when updating the email on the IMAP server -- however this also stopped us from archiving or deleting emails if either of these were disabled.
Adds functionality to reflect topic delete in Discourse to IMAP inbox (Gmail only for now) and reflecting Gmail deletes in Discourse.
Adding lots of tests, various refactors and code improvements.
When Discourse topic is destroyed in PostDestroyer mark the topic incoming email as imap_sync: true, and do the opposite when post is recovered.
* Fixed an issue I introduced in the last PR where I am just archiving everything regardless of whether it is actually archived in Discourse man_facepalming
* Refactor group list_mailboxes IMAP code to use providers, add specs, and add provider code to get the correct prodivder
Adds a imap_group_id column to IncomingEmail to deal with an issue where we were trying to update emails in the mailbox, calling IncomingEmail.where(imap_sync: true). However UID and UIDVALIDITY could be the same across accounts. So if group A used IMAP details for Gmail account A, and group B used IMAP details for Gmail account B, and both tried to sync changes to an email with UID of 3 (e.g. changing Labels), one account could affect the other. This even applied to Archiving!
Also in this PR:
* Fix error occurring if we do a uid_fetch and no emails are returned
* Allow for creating labels within the target mailbox (previously we would not do this, only use existing labels)
* Improve consistency for log messages
* Add specs for generic IMAP provider (Gmail specs still to come)
* Add custom archiving support for Gmail
* Only use Message-ID for uniqueness of IncomingEmail if it was generated by us
* Various refactors and improvements
