Sendmail on a LAN

[JD]

  On 08/17/2010 09:36 AM, Tim wrote:
> On Mon, 2010-08-16 at 15:24 -0400, Gregory Woodbury wrote:
>> Get a dyndns.com name for your router public ip address and set up at
>> dyndns to get mail delivered to that name.
> Of course, if your IP changes, then mail is going to get screwed up
> during the time it takes for next delivery attempt to go to your new IP
> address, instead of the old one.
>
> Dyndns, and other such things, are useful for giving yourself a hostname
> that you can control, to a static IP.  But aren't going to be much good
> if you have a dynamic IP.  Private webserving's easy enough with a
> varying IP, mail serving's another matter.
>
>
My router's public IP address is static. So that is not a problem.
But per other replies on  this list, it sounds like
a complicated puzzle to solve.
I have a dyndns name. and it maps onto my router's static IP
address. But I think at&t is blocking port 25.
I will have to talk to them and see if they will open it up.
I really need a tutorial on how I can accomplish this when
my sendmail machine is on a LAN.