[VM] IMAP message download fails sometimes

[Uday S Reddy]

Sometimes, when a lot of IMAP messages need to get downloaded, the download
fails in the middle with the warning message:

Retrieval from udrimap:INBOX signaled: 
    (vm-imap-protocol-error expected (BODY[] string) in FETCH response)

As far as I can tell, there is no bug in the code. If the uncompiled code
vm-imap.el is used, it works fine. Moreover, the code in question,
vm-imap-retrieve-to-target is the same as in VM 7.19.

It seems to be a race between the IMAP process and VM. The compiled code
probably runs faster and looks for the end of the message body before the
IMAP process finished delivering it. It always fails at the same message. So
it is reproducible.

Redoing vm-get-new-mail gets the remaining mail eventually.

Cheers,
Uday

Link to the bug report:

  https://bugs.launchpad.net/vm/+bug/897447