We have an environment set up with VMs and docker container. Now I have installed an SMTP Server with PTR Record bind to an IP and on the IP there is an VM running with a docker container on which there is an postfix server. (now that I write that down it seems quite complicated) I just wanted to know if there is any reason, why we should have any ports open for anyone outside our networks.


If you want to use that server only as a relay to send your mail outside you don't, But if there will be mail sent from outside to that server, then yes.

  • Thanks for your answer. We are just using it as an relay host. But our mails are still getting into some SPAM folders and I just recieved an message in our Log file, that we are "greylited" and have to try to send some mails later. I just wanted to make sure, that this is not a result of us blocking everything incoming... – John Daniels Aug 21 '18 at 6:31
  • Add it's IP to SPF records, check rev DNS. And yep, that's how most SMTP services fight with spam. – Alexander Aug 21 '18 at 7:15
  • Okay, thanks for your help, I forgot to change all SPF Records, which might have been the reason for those SPAM results – John Daniels Aug 22 '18 at 8:01

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