Comment 5 for bug 220991

I'm experiencing this problem but i has nothing to do with Thunderbird. The problem is that the IMAP service provided by Exchange is broken due to some exchange bug. You can check this by using another IMAP client, or even configuring an IMAP account in Outlook (if you can find a Windows computer, of course).

Thunderbird retrieves all message headers and you can even click on the message and see the message body. However, when clicking on the attachment, it hangs and never downloads. The server behaves in an unexpected way, by interrupting the response to the FETCH BODY command, which causes different behaviors on different email clients. Outlook, for example, miserably fails to even show the message content (if it contains an attachment), as it apparently attempts to download the whole message content every time you click on a message.

You can also check this from a telnet console. See below my telnet dump when attempting a direct dialog with the email server:

#################################
$ telnet mail.xxx.xxxxxxxx.se 143
Trying xxx.xxx.254.167...
Connected to xxx.xxxxxxxx.se.
Escape character is '^]'.
* OK Microsoft Exchange Server 2003 IMAP4rev1 server version 6.5.7638.1 (xxx.xxxxxxxx.se) ready.
. login myusername mypassword
. OK LOGIN completed.
. select inbox/test
* 1 EXISTS
* 0 RECENT
* FLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)
* OK [PERMANENTFLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)] Permanent flags
* OK [UIDVALIDITY 336144] UIDVALIDITY value
. OK [READ-WRITE] SELECT completed.
. fetch 1 rfc822.size
* 1 FETCH (RFC822.SIZE 67514)
. OK FETCH completed.
. FETCH 1 BODY[TEXT]
* 1 FETCH (BODY[TEXT]
#################################
(The last line is incomplete as it hangs here, where it is supposed to send the { character followed by the message size in bytes)

You can see a regular FETCH BODY response in the same server from a message NOT containing an attachment:

#################################
* 1 FETCH (BODY[TEXT] {1078}
This is a multi-part message in MIME format.

------_=_NextPart_001_01C8B5BE.9AD7282E
#################################

There seem to be a few reasons why Exchange would misbehave. Some of them are:

http://support.microsoft.com/kb/266286/en-us
http://support.microsoft.com/kb/835643/en-us
http://support.microsoft.com/kb/944153/en-us

I hope this helps.

Cheers,
Julian