How not to get people to open your emails

Email Compliance manager Skyler Holobach explains why you shouldn't act on clickbait advice you find on the internet.  Read more >>

Charter/Roadrunner bounces?

I'm pulling together information from various sources here, and using a bit of guess work. So keep in mind that this info is not guaranteed.

When sending mail to Charter/TWC/RoadRunner domains (full list here), are you seeing any of these bounces?

  • 550 5.1.0 sender rejected AUP#I-1310
  • 550 5.1.0 sender rejected AUP#I-1320
  • 550 5.1.0 sender rejected AUP#I-1330

These apparently correlate to the ISP's Cloudmark servers putting a sender into a rate limited "time-out" for anywhere from five minutes up to 24 hours. According to a post on Mailop from 2017, one bounce means 5 minutes, another means a one hour timeout, and the third means a 24 hour timeout. They might be listed in that order above, but I'm not sure.

Anyway, the net here is: In addition to investigating the underlying potential reputation issue (don't be a spammer, please?), you might want to slow down sending if getting the first or second error message. Perhaps throttle sending to trickle out over a number of hours instead of allowing as much mail to send as possible at any given second.

Information on dealing with Charter/Roadrunner deliverability issues is sparse (they no longer have a Postmaster site, alas), so I thought it'd be good to share this (best guess) information here with the hope that other folks will find it useful.

How Email Spam Filters Work Based On Algorithms

This is pretty basic stuff; it's not inaccurate, but it's not complete. Most other ISPs have other things going on that can also result in emails going to the spam folder. But as a starting point? It's not too bad. Check it out, from NBC: How Email Spam Filters Work Based On Algorithms.

Need example SMTP bounces for different ISPs?

Wondering what different kind of bounces an ISP might give to you? Postmark put together this handy-dandy SMTP bounce example lookup tool. It's called the SMTP Field Manual and it's pretty neat.

Spamhaus Blacklist Changes

Speaking of Spamhaus, this just popped up in my RSS feed reader. It looks like Spamhaus is going to take a harder stance against users who query their blacklists via open or public DNS systems (such as Google Public DNS or Cloudflare's 1.1.1.1 Service). They're going to respond to all queries from public/open DNS systems with a new 127.255.255.254 answer code, and respond to excessive queries from other sources with a new 127.255.255.255 response code. The net here is that if you query Spamhaus a lot, and aren't a registered, paying user, or if you use public DNS services for even your small hobbyist server, you're going to get cut off.

And based on the way this is implemented, it's possible that a bunch of legitimate mail will start bouncing before all Spamhaus users figure it out.

Even on my own hobbyist Linux box, I'm likely to run afoul of it. Instead of running my own DNS server, I just use Google's public DNS, and I use Spamhaus's "Zen" blacklist in my Postfix email server. Or at least I did, until I removed it from the configuration just now.

Stay tuned. I bet we're going to start seeing people popping up to ask why they're suddenly not receiving any more inbound mail.

Click here to head on over to Spamhaus to read the announcement.