How to set up a mail server if port 25 is closed?

Question

Exim

There are several nodes that host mail servers. Recently, the provider has blocked ports 25 and 465 for sending. I'm not going to change providers. There is also a node from another provider, which does not block anything. The task - to force to work mail through other provider. How can this be done with minimal setup of worker nodes with mail? Z.Y. All traffic cannot be forwarded. Mail must not only be received, but also sent.

Answer 1

In the case of postfix,
www.postfix.org/postconf.5.html#relayhost
will help You can specify a non-standard port for sending.
And for other mail servers there are similar options.