Executive Summary

Symptom: Fetchmail hangs when fetching messages. When it happens in fetchmail, it happens in Thunderbird as well.

Cause: Certain messages seem to cause the stbeehive.oracle.com IMAP server to hang when fetching headers with the IMAP (RFC-1730) FETCH 1 RFC822.HEADER command.

Resolution: This is a cheezy workaround: delete the message that causes the hang and it seems to unblock the rest of the fetching. You can do this in Thunderbird or with IMAP directly.

Details

For the past fifteen years I have been trying to avoid going quietly into that good night of using another email program other than my beloved and highly customized Emacs/VM. This means occasionally things will just stop working as the world around me changes and I try to stay the same (at least as far as MUAs go). This happened this week: fetchmail would hang. I observed that Thunderbird would hang also.

Diagnosis steps

  1. Enable verbose when fetching. 
    fetchmail -v -v -f fetchmailrc-oracle
  2. Observe the IMAP protocol interaction with the server. For example: 
    fetchmail: IMAP> A0122 FETCH 1 RFC822.HEADER
fetchmail: IMAP< * 1 FETCH (RFC822.HEADER {734}

    In this the case of this particular bug, it would hang on just such a header fetch.

  3. Experiment with direct IMAP interaction, using the IMAP protocol interation from the preceding step as a guide. Log in to the IMAP server with the following commands: 
    openssl s_client -crlf -connect stbeehive.oracle.com:993

    With this transcript:

    A0001 CAPABILITY
+* CAPABILITY IMAP4REV1 IDLE AUTH=PLAIN
+A0001 OK CAPABILITY completed
A0002 LOGIN "email address" <PASSWORD HERE>
+A0002 OK LOGIN completed
A0003 SELECT "INBOX"
+* 90 EXISTS
+* 0 RECENT
+* OK [UIDVALIDITY 4094122] UID validity status
+* OK [UIDNEXT 326362] Predicted next UID
+* FLAGS (\Seen \Deleted \Answered \Forwarded \Redirected \Flagged \Hidden \Draft $MDNSent)
+* OK [PERMANENTFLAGS (\Seen \Deleted \Answered \Forwarded \Redirected \Flagged \Hidden \Draft $MDNSent)] Permanent flags
+A0003 OK [READ-WRITE] SELECT completed
A0004 EXPUNGE

This technique enabled me to see what was going on.