I've been using Thunderbird as my email client on Window 7, via IMAP against my email provider's server, for some time. One annoyance I've had is related to the deletion of attachments.
I first noticed it with Thunderbird 3 (I think), with attachments in emails sent by Apple Mac users. The attachments could not be deleted; Thunderbird claimed they were, but the attachments were still in place. This was a known bug 351224 and fixed in Thunderbird 4.
However, I still had attachment deletion problems, but of a different kind. This applied to attachments sent from any MUA. If I deleted the attachments of an email, a duplicate of the email appeared in the Inbox, but minus attachments. The original, with attachments, copy was still present. I then had to manually delete the original mail. This is partly due to IMAP not offering a facility to delete attachments; the client has to delete the attachments from the body of the email and copy it back to the server. However, in performing this little dance, Thunderbird was not doing what I wanted.
I eventually tracked down a solution for this, which makes the behaviour acceptable. First, in "Account Settings->Server Settings", I changed the option for "When I delete a message" from "Move to this folder (Trash)" to "Just mark it deleted". This led to the next problem: If you use Unified folders (as I did), emails are not marked as deleted. You only see the deletion markup on selecting a real folder. I no longer use Unified mailboxes, but at least it is possible to either compact the Inbox to remove the deleted items, or just exit Thunderbird, if you select the option to "Clean up (Expunge) Inbox on Exit".
