I also have a problem with attachments.
When I enable Post By Email on the user area, a new email address was created.
If I send a email at that address with text and pictures everything is ok, but if i send a second email the pictures fail an I receive a email from wordpress where is saying that the file could not be moved to wp-content.
If I regenerate a new email address, the same problem, the first goes ok, the second not.
Any sugestion?
All the best.
Alex