Can I redirect port 25 with a dynamic dns service?

[richb at pioneer.ci.net (Rich Braun)]

dsr at tao.merseine.nu commented:
> You can't do it that way, but what you can do is tell dyndns.org
> to publish an MX record for you that points at a mail server
> which *will* relay for you.

Well, in theory a hosting service or ISP could assign a static IP out of one
of its blocks and set up a redirect which would relay packets the same way a
NAT router does.  (The DI-604 firewall thingie at my house is capable of doing
this.)

But in practice I have yet to see a company offer this type of service.  I
suppose IP addresses are scarce enough that the price point would be higher
than the store-and-forward relay service.  I'd like to see it, though:  it
involves much less prone-to-failure hardware between you & the rest of the
'net.

-rich