dovecot - Feb 2017 - Dovecot performance and proxy loops with IPv6

Ok, got it.

change imap-login and pop-login to these like showed in dovocot wiki for
high-performance login mode.

service imap-login {
        chroot = login
        service_count = 0
        client_limit = 600
        process_limit = 100
        process_min_avail = 16
}
service pop3-login {
        chroot = login
        service_count = 0
        client_limit = 600
        process_limit = 100
        process_min_avail = 16
}