SMTP

Using nc to interact with an SMTP server:

kali@kali:~$ nc -vz example.com 25

• Replace example.com with the domain or IP address of the SMTP server.

• Use port 25 for SMTP communication.

This command checks if the SMTP server on example.com is reachable on port 25. The -v flag provides verbose output, and the -z flag makes nc operate in scanning mode, checking for an open port without sending any data.

Using VRFY:

• Issue the VRFY command to verify the existence of a user or mailbox. Replace "user" with the actual username you want to check.

VRFY user

Resources

• https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol