Mail Archiver uses Sendgrid for sending internal emails (error reports, scheduler notifications and trial extensions). Sendgrid is updating the security. The internal emails require a new authentication with 5.3.3. You don't need to do anything because everything is handled by Mail Archiver.
All older version of Mail Archiver won't be able to send emails after the 7th of December. The rest of the functionality will continue to work.
If you need to use an older version then it's still possible to send the relevant information to Moth Software.
The Help menu has 2 entries "Show Session Logs in Finder" and "Show Crash Logs in Finder".
"Show Session Logs in Finder" gives you this result:
You should have less than 600 files. I usually need the newest 10 or so files.
"Show Crash Logs in Finder" goes to this folder. I need the files from Mail Archiver. Currently, I don't have any crash logs from Mail Archiver: