It looks to me that the venerable UW imapd is no longer capable of servicing multiple clients simultaneously to the same mailbox, which is weird, because I've done this very thing with it for years using what I believe is essentially the same setup as I have now. It's hard to imagine the point of making an IMAP server that doesn't properly implement this very ability that makes IMAP so desirable in the first place. But... many things have changed, I have new computers, different mail clients, etc, etc, who knows really what the problem is anymore.
So after months of putting it off, and having hit yet another rather embarrassing duplicated email incident in the last few days, I finally bit the bullet and decided it was time to fix this problem. Here is my previous setup, a standard, time-tested configuration:
- mbox-formatted mailboxes
Now, while I'd rather not switch to maildir, I wasn't completely opposed to it, but even if I did it presents the next question of how do I get my mail system to deliver to maildir mailboxes instead of mbox? Qmail and Postfix can do it, sure, but I didn't really want to change out my MTA since 1. I've been using sendmail forever and of course 2. this would be a big pain. Plus 3. based on prior experiences I don't really like Qmail. On the flip side, Postfix looks pretty cool, nice and lightweight--maybe I'll look at it again sometime in the near future. But what finally occurred to me was that Procmail could deliver to maildir mailboxes--and in fact I was already using it! So here is the improved setup:
- maildir-formatted mailboxes
- courier imapd
One week later: so far it's been working absolutely great. I can finally access my home email simultaneously from work and home and the two clients don't interfere with each other. In fact, as far as I can tell, they get along great. The problem with sending duplicate emails has gone away. And finally--an unexpected bonus--it's a LOT faster.
So thanks for many years of service, UW imapd, but I've had to move on.