
If you’re getting The message … could not be moved to the mailbox … in Leopard’s Mail.app 3.0 or 3.1, you might want to uncheck “Move deleted messages to the Trash mailbox” in Preferences >Accounts > (account) > Mailbox Behaviors.
Thanks to James in this thread.
Hang in there gang. Together we can work out the bugs in the Mail.app 2 to 3 transition.

May 30th, 2008 at 8:09 pm
Great. This helped me sort out my issue. Thank you.
June 29th, 2008 at 8:06 pm
I have this same problem, but unmarking the check did not fix it. It is a bug or something in the update for MAC OSX 10.5.3
Awaiting APPLECARE’S ASSISTANCE, or help from others. They want me to reinstall MAIL.app 3.3– the update caused it so I have my doubts that this will fix it. Perhaps there is another update for MAIL that is more compatible?
January 4th, 2009 at 4:10 pm
Version 3.5 (930.3) unchecking move to trash didn’t help.
Any further word?