Setting up Sendmail on a dynamic IP, part1: go through ISP’s SMTP

By Andrew Smith

I’ve been running my own mail (SMTP/IMAP) server for many years now and more recently decided to do something about all the retarded mail servers out there that classify messages from me as spam for no good reason. Typical corporate BS – “you’re not massive corporation like us so piss off”, but at the end of the day I’m the one who has to fix the problem.

The first thing I’ve had to do was make all the outbound email go through my ISP’s SMTP server. That’s because more than half of the receiving mail servers will indiscriminantly refuse anything coming from a dynamic IP. Cause why should you be allowed to run your own mail server from home? Pfft, ridiculous.

Luckily the fix wasn’t hard, a single line in sendmail.mc, which I had to compile into sendmail.cf as usual in Slackware. Here’s that line:

define(`SMART_HOST',`out.mnsi.net')dnl

That solved my problem for most cases and I’ve used the server that way for years and years. I don’t do a lot of business online, am mostly a recipient of email and not a sender. The people I do communicate with have mostly reasonable email servers that either accept my messages from the start or figure it out after the user tells them my mail isn’t spam.

But now I got a full-time job at Seneca College, with an IT department that loves big bad enterprise systems. The bigger the better. Which means many of my emails get filtered by this arcane spam decider as a matter of principle, despite hundreds of HAM messages received from me over years and years.

Hence the next (at least one) post in this series, part2: SPF.