I am running an OBSD mail server box, and running my own SMTP server along with it, but my ISP reserves port 25 for their own use (meaning they can't open port 25 for me even if they want to because they want it all for themselves
). I also cannot use my ISP's incoming and outgoing SMTP servers for some reason because they told me that I can only use those servers for internal e-mails, i.e. I can only send/receive from @myisp.com addresses (e-mails only from my ISP's domain).
So are there any alternative methods where I can use a port other than 25 to receive e-mails on my server? I can send e-mails fine, since any outgoing port will work and by default it will send to port 25 of any other e-mail server, but say if my email@example.com
tried to send me an e-mail, I would not be able to receive it because it will try to send the e-mail to my server at port 25 by default, but my port 25 is blocked. Or are there any other ports that all e-mail servers try to send to besides 25 (like 8080 besides 80 for http, which is how I configured my website because my ISP also blocks port 80 so I put Apache on port 8080 and everyone can see my website)?