Is it at all possible to run postfix with normal SMTP port 25 active and mail-receiver for Discourse on the same host, somehow, with some clever configuration?
Ideally I want to run postfix on the server as per normal, and not be constrained by Discourse taking over SMTP port 25.
yes, it is possible, although not recommended as prone to more config errors 
(and you’d need nginx or other front proxy configured as well…)
That worked for me:
Thanks, but I dont see how that answers the question. I have Discourse, and mail-receiver and I am familiar with a lot of Postfix and Dovecot, but I am aksing how I can get mail intended for Discourse routed by Postfix to mail reciever without interfereing with normal SMTP port 25 on the server. An yes I run Discourse reverse proxied with nginx.
Not being recommended is not a useful response, because then it means you have to have a dedicated server to only run Discourse and you cant run normal mail on it, if, as I need, you run mail-receiver for inbound email submissions. As to ‘config errors’ that is my responsibility and I am capable of dealing with that.
What I don’t know is the approach to take. Something with LMTP to mail-receiver on a different port?
When you say it worked for you, is this the scenario you have? If so, can you give more specific detail?
Thanks!
Oh I’m sorry I’ve read your question far too quickly
You can have the discourse receiver bind to an ipv6 address (wrap the address in square brackets) and the external postfix act as a relay. It’s a little fiddly, as you have to make sure that the external postfix doesn’t bind to the ipv6 address, but it sounds like you can figure it out. I just did this to be able to run 15 mark receivers run on a single host (though only one is running now).