I am setting up a backup SMTP server which is located outside of our offices.

The idea is that it should accept all messages addressed to our domains (DNS metric is high, so this should happen only when internal smtp servers are down), and forward them to our internal smtp servers, when they are back up (in reality, it will try to do so every few hours).

I have created a transport map

example.com smtp:[ip of smtp server]:25
example2.com smtp:[ip of smtp server]:25

and I have set main.cf

default_transport:discard:Outgoing email disabled on this node
relay_domains =

The problem is that, when connecting via telnet, postfix still accepts messages addressed to any domain

When connecting via thunderbird, postfix works properly.

I'm not sure how to interpret this.


What is the value of mynetworks on main.cf file? If you do the telnet test using a host that is on mynetworks, it will be accepted. See http://www.postfix.org/postconf.5.html#mynetworks

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  • Apparently, I had a low IQ moment. I was telneting to localhost. Thanks – Tomislav Plečko Feb 15 '19 at 14:56

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