One way is to use https://doc.dovecot.org/configuration_manual/authentication/auth_policy/

or you can use 

passdb {
  driver = passwd-file
  deny = yes
  args = username_formar=%{rip} /etc/dovecot/deny.ip
}

or you can use https://doc.dovecot.org/configuration_manual/authentication/lua_based_authentication/

and write this in Lua.

Aki


-------- Original message --------
From: Hippo Man <hippoman@gmail.com>
Date: 8/1/23 18:14 (GMT+02:00)
To: dovecot@dovecot.org
Subject: Forcing imap authentication failure for certain IP addresses

I'm running dovecot 2.3.18 under Debian 11.

I want to do something that's a bit unusual: when IMAP connections are attempted
from a few specific IP addresses, I want to force an IMAP authentication failure
from those connections, no matter what user ID and password are specified.

I know that I can use iptables to completely block imap access from those IP
addresses to the IMAP ports. However, in these specific cases, I'd prefer that
the connection goes through to dovecot, but for dovecot then to always generate
authentication failures for those specific connections ... even if a valid
user ID and password happen to be specified.

Is there a way to do this in dovecot?

Thank you very much in advance.

--
 hippoman@gmail.com
 Take a hippopotamus to lunch today.

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