"over quota" message listed as cause for Failed Delivery

Control-click on the .mac Inbox, and choose Get Info. Then in the resulting window choose the .mac account and the Quota Limits tab -- what does it report for the space used by each folder?

If you go into .Mac in your browser, check your account settings for storage, what is reported. With the new 10 GB of storage provided to basic accounts, it would not seem likely you are over quota, unless allocated mostly to iDisk and not to Mail.

Ernie

But don't "over quota" messages pertain to your recipient's mail server and mail account? I've never heard of the sender's mail account kicking out a "sender account over quota". Read the message carefully. I suspect that it says in there somewhere that your recipient's imap or pop server reported that the recipient's mail account is over quota to the .mac smtp server, who reported it to you. The recipient needs to clear some mail off his/her mail account, to free up enough space. The mail message may have been queued in the .mac smtp server while redelivery attempts would be tried periodically for some finite amount of time. Many mail servers will temporarily queue mail that cannot be immediately delivered. Once your recipient made adequate space, then at the next periodic delivery attempt, .mac smtp server could send them because the recipient's pop or imap account now had adequate storage space.