postfix open relay

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Hi redhat support,

i just would like to ask how can i check or verify that open relay is active in our smtp server.

thanks.

Responses

The basic steps are:
Connect to SMTP server from an external host (ie. outside your local network that hasn't been configured to allow relaying) and attempt to send an email to a domain that your postfix server doesn't accept mail for (ie. it's not your domain).

Here is an example attempt to send from your mail server to a third party destination:
telnet smtp.yourdomain.com 25 (your externally exposed SMTP server)

helo yourdomain.com
mail from: something@yourdomain.com
rcpt to: something@notyourdomain.com

You should now get a "554 Relay access denied", if you get a "250 Ok" or similar, your server is going to relay.

The 'rcpt to' portion should only accept mail addressed to addresses @yourdomain.com

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