Фильтр для sendmail
[Definition]
failregex = [<HOST>] .*to MTA
[<HOST>] .* Mailbox disabled for this recipient
[<HOST>], reject.*… Relaying denied
(User unknown)n* [<HOST>]
badlogin: .* [<HOST>] plaintext .* SASL
Отличная штука этот fail2ban 🙂