Service unavailable, lots of idle dovecot-login processes

[Wolfgang]

Hi,

Web search turned no results to this problem:

We have a small site running private e-mail for maybe 12 people, dovecot
is used by Postfix-SASL and IMAP clients.

PROBLEM: When starting dovecot, after a few hours, IMAP clients are no
longer able to connect. Thunderbird indicates that connection is refused.

On the server, we see 100 dovecot/imap-login processes. This is the
process limit. If we increase the process limit to 200, same thing, we
survive a few hours longer but eventually we're seeing 200 imap-login
processes and rejected connections.

When listing TCP connections via lsof, there are only around 30
connections open to IMAP and we have exactly the same amount of
dovecot/imap processes. These connections are held by 30
dovecot/imap-login processes.

The other 70 dovecot/imap-login processes seem to do nothing. They're
all sitting in "epoll_wait(14," according to strace but don't have TCP
connections open.

The only way out of this that we have found is re-starting dovecot every
few hours.

BTW, service_count = 1 for improved security.
Dovecot Version: 2.3.4.1 (f79e8e7e4)

Interestingly we were using nearly the same config on our old server
with 2.2.13 and did not see this issue.

Any ideas how to solve that properly?

Thank you,
Wolfgang