Fail2ban does not block failed login attempts to Plesk Premium Email webmail.

Plain Roundcube is blocked by jail plesk-roundcube after failing all attempts to log in.

If the webmail is switched to Plesk Premium Email, the jail plesk-roundcube does not block failed attempts.

As a workaround create the following filter:

cat /etc/fail2ban/filter.d/kolab-webmail.conf
[Definition]
failregex = ^[\d{4}-[A-Za-z]{3}-\d{2} \d{2}:\d{2}:\d{2} +\d{4}]: <[^>]+> Failed login for .* from <HOST> in session .*

ignoreregex =

Also add the jail into /etc/fail2ban/jail.d/plesk.conf:

[kolab-webmail]
enabled = true
filter = kolab-webmail
port = http,https
logpath = /var/log/roundcubemail/userlogins.log
maxretry = 1
findtime = 600
bantime = 3600
backend = auto