tcp/25 smtp

> smtp-user-enum -U /usr/share/wordlists/dirb/others/names.txt -M RCPT -t <ip>
> perl smtp-user-enum.pl -M VRFY -U /usr/share/seclists/Usernames/Names/names.txt -t <ip>
> nmap --script smtp-enum-users <ip> -Pn