SEC-06 / SECURITY
Open Relay Test
Test whether a mail server will relay mail from an external sender to an external recipient — the open-relay misconfiguration that spammers hunt for and abuse.
About the Open Relay Test
An open relay is a mail server that forwards email from any sender to any recipient, regardless of whether either belongs to it. Spammers actively scan for open relays to launder their traffic. This tool safely tests whether a server relays external mail — without ever sending a message.
What this tool checks
It opens an SMTP session and attempts to set an external sender and external recipient, then reads whether the server accepts the RCPT command. It stops before any mail is sent.
Why open relays are dangerous
An open relay lets anyone send mail through your server, which quickly gets your IP blacklisted and can implicate you in spam campaigns. Relaying should be restricted to authenticated users only.
Frequently asked questions
What is an open mail relay?
An open relay is an SMTP server that accepts and forwards mail from any sender to any recipient without authentication. It's a serious misconfiguration that spammers exploit.
How do I fix an open relay?
Configure your mail server to only relay for authenticated users or trusted local networks. Every modern mail server supports this; check your relay and authentication settings.
Does this tool send spam?
No. It only tests whether the server would accept an external relay attempt by reading the response to the RCPT command, and never transmits an actual message.