So my ISP start blocking all *inbound* traffic on port 25 to avoid the exploit of poorly configured servers. I ran a mailserver for quite some time and without notice I was cut off early August 2002.

My first 'solution' was using Eric S. Raymond's fetchmail. My domain name registrar let me choose to define a MX host for my mail, or to have all mail forwarded to an existing pop account. So I changed it to the latter and let fetchmail empty that pop box on a 15 minute interval from my mailserver. Fetchmail examines the headers of every individual e-mail, rewrites the headers and submit it to localhost which was cut off in the first place.
This works quite nice, but has some side effects like BCC's which couldn't be resolved anymore and ended up in the 'main' account. Still, it works out fine, provided that you have an e-mail account you can use. I had one which came with my ISP.

So I stumbled upon no-ip.com. They provide a mail-reflector which reroutes e-mail to a port of my choosing. So I made them the primary MX host for my domain and let my mailserver listen on a high-port. Works like a charms for over a year no without any problems. I'm sure there are others who provide similar services.

Martijn