SMTP Relays...

From: Patrick/VCM SysOp <patrick_at_vintagecomputermarketplace.com>
Date: Thu Sep 2 12:12:29 2004

> My sister's ISP just started doing that (cablevision...
> probably the same
> NY ISP you are referring to). She now has to have two
> different account
> setups. One for when she is home and wants to send email, and one for
> when she is traveling and wants to send email.

Too bad the mail client (and/or OS) doesn't have a provision for querying
DHCP, which can provide an SMTP server response to be used while on the
connected network. I view that as a short-coming of the OS, the MUA, and
the SMTP protocol.

That said, I have the same issue with my ISP (Earthlink) when I use dial-up
while on the road. I have been able to solve this problem by exploiting the
fact that most networks have a host named "mail" in their domain that will
relay from it's network-local addresses (like it's DHCP-assigned addresses).
Emulating the above behavior, then, is as follows: I specify simply "mail"
as the SMTP server name (with no domain name) in my MUA, and configure to
allow the connected network's DHCP server to provide the domain name and DNS
servers for the connection. I set up my own network so that my MTA has a
CNAME (alias in the Windows world) named "mail" as well, so I don't have to
change config when I'm at the office. Now, I can connect with my office
Ethernet or using Earthlink dialup without changing my MUA config. And,
about 80% of the time I use a hotel's broadband connection, I am able to get
a usable server that allows me to send mail without filtering or relay
block, without changing my MUA config.

Of course, you can also set up a VPN connection to your network or MTA, but
that's another can of worms.

I think the ISPs are right to block outbound port 25, and I hope they do
more of it. A high percentage of the spam that's being blocked by my
filters is coming from "dynamic" connections (cable, dial-up, DSL) that make
it harder to trace and block on my side, and harder for the ISP to clamp
without affecting the next poor customer who gets that IP address. The fact
that people have trouble configuring it is a matter of education of the
consumer and corrections of shortcomings in the MUAs (not making use of
vital information in available protocols). But in my mind, blocking it is
no worse an offense by the ISP than seat belt laws, traffic lights, or
control towers at airports. And the ISP (or the corporation you work for,
etc.) has a right to control its traffic, especially when they are being
made increasingly responsible for that traffic by their peers.

--Patrick
Received on Thu Sep 02 2004 - 12:12:29 BST