As I see a lot ISP's are blocking their routers on tcp port 25 but leave tcp port 587 to do SMTP/SMTPS job.
Virtualmin installs Postfix to listen on both ports 25 and 587.
1) If port 25 is blocked can I get email to/from outside on port 587 automatically? Are mail servers which communicate only on port 25?
2) Is it a good idea to use in router iptables for prerouting port 25 forwarding to port 587? In this way a mail server which uses only 25 port for delivering email and not 587 can deliver the message into the mail server.