Thunderbird with Enigmail on IMAP

If you are working on an IMAP Server and using Enigmail to crypt and decrypt mail you may encounter a problem with decoded attachments. OpenPGP is not able to decrypt the whole message since the attachment is loaded on demand. If you want to change this just set this settings in you mail client installation:

user_pref("mail.server.default.mime_parts_on_demand", false);