Some users had complained that Mail Archiver didn't move the mails to the trash for Mail. I had problems reproducing the issue but finally I was able to kill the bug.
Bugs come in a wonderful variety. We developers don't like bugs. My code is perfect. How can it have bugs?
Then there is Mail which likes to look perfect. Everything seems to happen immediately. Move thousands of mails to another mailbox. Done. From observing Mail I know that this is faked.
The problem was that a couple of users had complained that nothing happened when Mail Archiver was supposed to move mails to the trash at the end of archiving. No error message. Just nothing happened.
Whenever I tried to reproduce the issue I found nothing. So the issue got rejected again.
Until the problem got reported again.
I thought to myself: something must be there. How about checking in AppleScript if the mail actually got deleted?
Bingo! This showed me the problem.
This is Mail trying to look perfect. Mail Archiver is telling Mail to move a mail to the trash. When Mail is busy with something then the command gets dropped. Starting with 4.2 beta 4 Mail Archiver now tries a couple of times. If it doesn't succeed then you get an error message.