Always use your "home" SMTP server to send e-mail, using SMTP AUTH
and submitting using port 587/submission.
This is a bit of work to setup, but not much and well worth the effort.
Dan Barker wrote:
I see how SPF records can help if you are at the office. What about when you
are on the road?
You will connect to the 'net via your cellphone, a dial-up, or a wireless
network. Most likely, the ISP won't route port 25 traffic to your "home"
system's SMTP servers, so you must use the remote ISP's SMTP servers. They
have no idea who you are, and your home server has no idea from where you
might connect.
I just don't see any way around this except using a cumbersome "remote
control" program (NetOp, Remote Desktop Connection, SSH, telnet, Terminal
Services, PC Anywhere) to access your "home" system for any outbound email.
That's just not workable.
Example:
dbarker(_at_)visioncomm(_dot_)net
At home, SMTP is mail.visioncomm.net.
On the road, I plug my cellphone into my laptop and connect to
smtp.sprintpcs.com (outbound and mail.visioncomm.net inbound). Sprint won't
route SMTP to mail.visioncomm.net so I send as
dbarker(_at_)visioncomm(_dot_)net using
their SMTP server.
The only work-around I can imagine is if all ISP's update their SMTP traffic
filter to check if the Reply-To address's home system is SPF compliant, and
only if so allow the remote user to pass SMTP traffic home. I'm not sure I
know how to do that with iptables<g>.
Dan Barker
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dtaylor(_at_)vocalabs(_dot_)com http://www.vocalabs.com/
(952)941-6580x203