SMTP Open Relay Test
Check if a mail server is an open relay that could be exploited by spammers to send bulk email.
SMTP Relay Test checks whether your mail server is an open relay (sends mail from any sender). Open relay = blacklist listing within 24 hours. The tool performs a test connection + AUTH probe and gives recommendations.
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What is an SMTP Open Relay?
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.
Related guides
Longer-form reading on this topic from the knowledge base.
Email deliverability monitoring
Alerts on MX / SPF / DKIM / DMARC changes — guard against silent email infrastructure breakage.