- Added `ImapFindSentMailboxService` to replace utility function it
fixes an edge case where special flag `Sent` folder may have zero
messages, we fall back to regex based approach to find other candidates
- Fixed edge case where some servers may not return text content for
body it parses the HTML in that case
- Some other enhancements with capability based detection
Tested with Stalwart server and Titan email
/closes #13884
