Partial sync only has to FETCH flags, nothing else

[ChristophWurst]

Is your feature request related to a problem? Please describe.

Partial sync can be expensive without QRESYC/CONDSTORE capabilities. Horde will flag all given UIDs as changed. We then fetch the messages another time but only really use the flags and tags data to update the cache. Headers, subject, imapdate, etc are fetched without a purpose.

Describe the solution you'd like

Adjust \OCA\Mail\IMAP\Sync\Synchronizer::sync to call a minimal version of \OCA\Mail\IMAP\MessageMapper::findByIds for changed message flags.

Describe alternatives you've considered

No response

Additional context

No response

[ChristophWurst]

This would be worth the effort.

Excluded from FETCH in \OCA\Mail\IMAP\MessageMapper::findByIds are imapDate and headerText