Thou Shalt Honor RFC-822, Or Not Read Email At All (08 Nov 2009)

With the excellent tutorial Accessing IMAP email accounts using telnet at hand, getting up to speed with IMAP was a matter of minutes. Digging into the protocol was pretty cool (in my very own sick and geeky sense of coolness), and I learned a few things. It seems that Exchange Server, when contacted via IMAP, tries to convert all messages into RFC-822 format, and when this fails, said error is reported. So as far as I can tell, this isn't really an email client issue, but rather a problem in either the original message data or in the conversion process on the server.

However, those insights didn't solve the problem right away. I tried deleting a few suspect messages by ID, without seeing much of an improvement. After a while, I resorted to a more radical experiment:

• Create a temp folder on the IMAP server
• Move all messages from the Inbox to the temp folder
• With all inbox messages out of the way, hit Thunderbird's "Get Mail" button again.

You'd think that with an empty inbox, there shouldn't be a reason anymore for error messages - but still, Thunderbird kept reporting RFC-822 conversion issues.

Thunderbird glitch? Bad hair day? What was going on?

Desperate as I was, I did something which, being a Thunderbird devotee, I would never do under normal circumstances: I ran Outlook. And indeed, to my surprise, Outlook still displayed a number of messages in my inbox! All of those were meeting invitations. Apparently, those were the messages which were in some way incompliant or at least incompatible with RFC-822. I deleted all those messages in Outlook, emptied the "Deleted Items" and "Trash" folders, then ran Thunderbird again.

Argl. "Get Mail" still reports the same error messages.

Another telnet session followed:

  telnet int-mail.ptc.com 143
  . login cbrod JOSHUA
  . select INBOX
  . fetch 1:100 flags

Surprisingly, IMAP still reported 17 messages, which I then deleted manually as follows:

  . store 1:17 flags \Deleted
  . expunge
  . close

And now, finally, the error message in Thunderbird was gone. Phew.

In hindsight, I should have kept those invitation messages around to find out more about their RFC-822 compliance problem. But I guess there is no shortage of meeting invitations in an Outlook-centric company, and so there will be more specimens available for thorough scrutiny