TCP 25, 587: SMTP

The Simple Mail Transfer Protocol is a communication protocol for electronic mail transmission. As an Internet standard, SMTP was first defined in 1982 by RFC 821, and updated in 2008 by RFC 5321 to Extended SMTP additions, which is the protocol variety in widespread use today.

-- Wikipedia

Related

SMTP and POP3 commands

Enumeration

Connect

nc -nv <ip> 25

Verify users

Manually

VRFY <user>

-> 250 success, 550 not found

Automated

/usr/share/legion/scripts/smtp-user-enum.pl -M RCPT -U <users-file> -t <ip>

Automated #2

for user in $(cat users.txt); do echo VRFY $user | nc -nv -w 1 <ip> 25 2>/dev/null | grep ^"250"; done

Metasploit modules

• smtp_version

• smtp_enum

Nmap scripts

• smtp-brute.nse

• smtp-commands.nse

• smtp-enum-users.nse

• smtp-ntlm-info.nse

• smtp-open-relay.nse

• smtp-strangeport.nse

• smtp-vuln-cve2010-4344.nse

• smtp-vuln-cve2011-1720.nse

• smtp-vuln-cve2011-1764.nse