Check if a mail server is an open relay that could be exploited by spammers to send bulk email.
An open relay is an SMTP mail server that accepts and forwards email for any sender and any recipient domain — not just its own users. Spammers exploit open relays to send bulk email while hiding their true origin. A correctly configured mail server should only relay messages for authorized users or domains it controls. Running an open relay leads to IP blacklisting, abuse complaints, and potential legal issues.