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Postfix newbie question: If I use the default, relay_transport = relay (by commenting out the error line), does that make me an open relay? Or does the inet_interfaces fix it?

inet_interfaces = loopback-only
# default_transport = error
# relay_transport = error

In general, can someone clarify what these two flags do? I have a hard time understanding the documentation.

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If you want to verify either way there are a couple of open relay testing tools which should help.

Heres a couple:

Network abuse clearing house

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It appears neither of those sites work anymore. The site was taken down some time ago. – Chris S Aug 18 '14 at 17:44

The default value of relay_transport is relay. So as per the documentation, mails will be delivered to the domains listed in relay_domains

Now what is relay_domains? - Destination domains and subdomains the system will relay mails to.

The default value for relay_domains parameter is $mydestination

The default value for $mydestination is localhost, so the mails are deliverd to the same system.

That implies you don't have an open relay.

P.S. Any postfix gurus around? CMIIAW

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