Here is my problem...
I want to host my own email server at home with a dynamic IP. Thank you for your free dynamic DNS service, which solves the problem of the dynamic IP.
Another problem is that my ISP is blocking incoming SMTP (port 25). I have configured the router to accept the connection to port 200 and forward to internal server port 25. It works fine. Now I want a solution to forward all incoming mail to port 200 on my mail server. I saw your email store/forward service, is it the right solution for me?

Email store/forward service is the right solution for you. You can host your email server on a non-standard port(in your case, 200) and receive emails for your domain name via our email servers. Our email servers will receive emails for your domain name and forward them to your email server on port 200.

To be able to do that, you need to

1. Sign up for email store/forward service at https://www.dynu.com/Controlpanel/AddEmail

2. Specify the ETRN host and port in the control panel. ETRN host is the hostname of your email server, ETRN port being the non-standard port on which your email server is running. In your case, 200.

3. Host your email server on port 200, and setup port forwarding in your router to accept the connection to port 200 and forward to port 200 on your email server internal port.

4. List mx1.dynu.com and mx2.dynu.com as primary MX records for your email server.