iSMTP

iSMTP is designed to test SMTP servers for vulnerabilities related to user enumeration, email spoofing, and open relays. It helps security professionals identify misconfigured SMTP services that could leak valid usernames or allow unauthorized email relay and spoofing. The tool is particularly useful in penetration testing scenarios where assessing email server security is required.

Use cases include enumerating valid user accounts via VRFY or RCPT TO commands, checking for internal spoofing capabilities by crafting custom sender and recipient details, and verifying external relay permissions. It supports testing single hosts or lists of SMTP servers from files, making it efficient for batch operations.

The tool outputs results clearly, marking valid users with [+ success] and invalid ones with [- invalid], and can save detailed logs to files for further analysis.

iSMTP connects to SMTP servers on specified IP:port addresses and performs protocol-level tests. For enumeration, it uses SMTP VRFY (type 1) or RCPT TO (type 2) commands against a dictionary of usernames, analyzing server responses to distinguish valid from invalid users. Spoofing tests involve sending custom MAIL FROM, RCPT TO, and sender names to check internal relay policies. Relay testing sends emails to external domains to detect open relays. It supports timeouts and combines tests in any order.