I want to host my own (postfix) mailserver for my domain "mydomain.com". For the unlikely event that my server is down, I would like to have gmail.com receive all mail and forward it to my domain.
Complicating factor is that my ISP does not allow incoming traffic on port 25. So I managed to set-up via Zoneedit that mail from domain 2555 is forwarded to 25 via a separate domain "myseconddomain.com"
So I set it up in the following way:
- I have a forward all mail from mydomain.com to my gmail account
- I set up gmail to forward my mail to email@example.com
- Mail from myseconddomain.com is via a special set-up sent to my server on ip-address w.x.y.z port 2555.
- My local firewall makes sure that traffic from port 2555 is forwarded to port 25.
In theory (and partial in practice), this whole chain works. The problem is that some mail is not delivered to my mail server, but other mail is. I can see this in my gmail account because it saves copies of all my mail.
Why is that?