Here's everything after I enabled auth_verbose, auth_debug_passwords and auth_debug.

Apr 06 16:20:47 auth(default): Info: new auth connection: pid=27885 Apr 06 16:20:47 auth(default): Info: client in: AUTH 1 PLAIN
service=imap secured lip=184.82.40.118 rip=193.255.135.1
lport=143 rport=52150 Apr 06 16:20:47 auth(default): Info: client out: CONT 1 Apr 06 16:20:47 auth(default): Info: client in: CONT 1
AGJpbGdpAGJpbGdpOTg3 Apr 06 16:20:47 auth(default): Info: passwd-file(bilgi,193.255.135.1): lookup: user=bilgi file=/etc/dovecot/passwd Apr 06 16:20:47 auth(default): Info: passwd-file(bilgi,193.255.135.1): unknown user Apr 06 16:20:49 auth(default): Info: client out: FAIL 1 user=bilgi Apr 06 16:20:54 auth(default): Info: client in: AUTH 2 PLAIN
service=imap secured lip=184.82.40.118 rip=193.255.135.1
lport=143 rport=52150 resp=AGJpbGdpAGJpbGdpOTg3 Apr 06 16:20:54 auth(default): Info: passwd-file(bilgi,193.255.135.1): lookup: user=bilgi file=/etc/dovecot/passwd Apr 06 16:20:54 auth(default): Info: passwd-file(bilgi,193.255.135.1): unknown user Apr 06 16:20:56 auth(default): Info: client out: FAIL 2 user=bilgi Apr 06 16:21:06 imap-login: Info: Disconnected (auth failed, 2 attempts): user=<bilgi>, method=PLAIN, rip=193.255.135.1, lip=184.82.40.118, TLS