I was trying to run two instances of dovecot on the same machine, each listening on a single IP. The problem I ran into was that each time one was started or restarted, the other stopped responding. I saw the following in the logs:

Mar 23 00:02:27 sentinel dovecot: Dovecot v1.0.rc27 starting up Mar 23 00:02:27 sentinel dovecot: Socket already exists: /var/run/dovecot/dict-server

After I saw that, I commented out the dict section and quota from the plugins. The second line disappeared, but I could still only get one dovecot listening at a time. In the end, I went back to a single dovecot listening on all IP's, and found another way to do what I was trying to do, so all is still working for me. I'm guessing I'm the first person to try to run two dovecots on one machine.

Actually, I should clarify: there was also a third, listening to none on localhost, but there only for the lda process. The auth socket was set to /var/run/dovecot/auth-master. And this also was not accepting connections while the others were running.

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