Describe the bug
How can i increase client_limit, currently my mailcow server keep stop running and imap_login get error, users cannot login

But your limit looks way lower. I wonder why.
Maybe this isn't even related for anvil?
There are other people with that issue tho: https://www.dovecot.org/list/dovecot/2010-November/054517.html
We increased those limits a while ago. Checkout dovecot.conf from origin/master via git. :)
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Most helpful comment
We increased those limits a while ago. Checkout dovecot.conf from origin/master via git. :)