On 11/5/03 4:49 PM, Allen Watson deftly typed out:

> David's suggestion is an excellent one, but I ran into an added problem when
> I tried it. My ISP, Earthlink, no only prevents me from using SMTP servers
> outside their domain; when I am connected to the Internet through them, I
> cannot use the SMTP server on my Mac!! On the other hand, I've corresponded
> with people who are doing this regularly, and report that they give
> themselves much speedier service than their ISP would.

There are two methods employed by ISPs for controlling what mail traffic
leaves their network:

- blocking mail with a return path that doesn't match the ISPs domain
(i.e. A message with a From: containing an Earthlink email account while
connected to the Internet through Verizon)
- blocking TCP and UDP traffic on port 25

In the first case you are only allowed to send mail through the ISP's mail
servers if the From address matches the ISPs domain. I believe Verizon, at
least in my area, does this. In the second case, port 25 is the port SMTP
traffic usually travels through, so, by blocking it, the ISP is trying to
ensure that all mail sending goes through their mail server (so that they
have a record of it and can track it). Both of these are measures they take
to control/restrict the spam coming out of their networks.

If your ISP only does the first (return-path verification), you *can* send
mail...you just have to select an account that belongs to the ISP to send
with. If your ISP does port 25 blocking, then using an external SMTP server
or running a mail server on your machine will avail you nothing since that
mail server will try to communicate with others via port 25 and will get
blocked.  

In my case, since I control the mail server at the company I work for, I've
added an additional SMTP listener on our mail server at port 2025 and
configured my accounts to send via that custom port. This way I can connect
to it from anywhere, whether the ISP is blocking port 25 or not.

-Remo Del Bello 

-- 
"Yet even the most subtle spiders may leave a weak thread."
- Gandalf the Grey in "The Lord of the Rings: The Fellowship of the Ring"

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