Resources Home / How Email Firewalls Work

How Email Firewalls Work

Spam filters need spam filters now

By now, most email marketers know you should avoid using "spammy" phrases like "FREE! CLICK NOW!" or the spam filters will trash your message (see: How spam filters work).

But did you know that before your email even gets to a spam filter, it has to get through a gatekeeper? Yep, spam is so bad, that spam filters now need spam filters to help them.

These gatekeepers kinda look like this:

Ironport Gateway

Looks vicious, doesn't it? They're all over the place. ISPs use them. Large corporations use them. Small businesses are starting to use them.

What's really scary is they all talk to each other. It's how they learn what "spam" is, and who should be blocked (Gulp - are they talking about you right now?).

That's a picture of IronPort's Email Security Appliance. If it thinks your email is spam, it'll gobble it up and fart its remains into cyberspace before your recipient's puny little spam filter even gets a chance to look for the word "V1AGRA". It won't even waste the energy to tell anybody about it (like in a bounce report).

Ever send to your email list and wonder where 5-10% of the emails seem to disappear off to? Ever wonder why the numbers don't seem to add up in your deliverability reports? It was probably one of these big, mean appliances (ReturnPath says its closer to 20% in this PDF Report).

If IronPort thinks your email is "not spam" then it lets your email through (but it'll still get analyzed by a content-based spam filter). And that's when your "avoid spammy content" tactics finally come into play.

To learn more about how IronPort works, they've got an eyebrow-raising demo you should watch. Click the tab at the bottom of the movie, to skip to the "anti-spam" section. Watch the demo

How the heck does this server know what spam is? Your own recipients teach it. When you send an email to your list, and someone on your list thinks it's spam, or doesn't remember opting-in to your list, or if you purchased a list from someone, that person can report you to SpamCop (which was purchased by IronPort in 2003, and is now called "SenderBase"). Get enough SpamCop complaints, and they'll propogate your data to all the IronPort servers around the world, letting everyone know you're a spammer: Senderbase

Incidentally, your email service provider should be registered at SenderBase, so they can properly investigate every single complaint generated in response to their users' campaigns. At i-Emailer, everyone on our staff personally receives copies of any complaints that come in, so we can go suspend the sender's account and investigate immediately.

IronPort is only one of many, many email firewalls, gateways, and security appliances you, as an email marketer, should learn about. Also see:

All of those big, mean, ruthless "gatekeepers" rely on "reputation" scores to block emails before they even get to the content-based spam filters.

So you really want to make sure your reputation is good. How can you do this?

  • Never send spam.
  • Don't buy lists. Don't use lists that other people gave you.
  • Only send to lists of people who know you, and requested emails from you. Otherwise, if you want to get the word out about your company, pick up the phone and call your prospects, or pick up a pen and write them. Or, email them one at a time (see "Definition of spam" and specifically the word "bulk"), from your own email program.

Assuming you're not sending spam, your email design is a huge factor in getting you blocked by one of these gatekeepers:

  • When you send emails, always include a "How we got your email" reminder. i-Emailer's built-in templates include that information for you, with our *|LIST:DESCRIPTION|* tag. This tag is automatically replaced with the survey information that you provide each time you setup a list in i-Emailer.
  • Your email designs have to be reputable looking. Get sloppy, and people won't trust your opt-out link, and report you instead. See how one designer got blacklisted from his design.
  • Always include a one-click unsubscribe link in every campaign you send (i-Emailer adds this for you when you use our built-in templates. If you use your own designs, we'll give you a code snippet).
  • Haven't contacted your list in a while? Or is this your first campaign? Send an introduction email. Remind them of who you are, or you'll get a big surge in complaints, and wind up on all those ugly blacklists out there.
  • Sometimes, you're not the one who got you blacklisted. It was someone else on the server that you used. If you used a shared email marketing service like i-Emailer, where thousands of people are sending emails from the same IP, you're at risk. That's why i-Emailer has lots of IPs that we send from, but more importantly, we have a human staff of reviewers who pre-screen all new users before they're allowed to use our system. If a user still manages to generate spam complaints, our abuse desk can shut the user down immediately, and re-route email to our other IPs, while we deal with the blacklist service. This is how we manage to send millions of emails every day from our system. If that still sounds too risky, or if you hate sharing, get your own dedicated IP address from i-Emailer.
  • But if you think you can send junk, get reported, then switch to a new email server, you are sadly mistaken. Once you get reported, your company's name and domain name are on the lists. They'll know to block ALL emails with your name in it from now on, no matter who sends it, or where it came from. This is why affiliate marketing programs can be so risky. Imagine thousands of sloppy email senders (your affiliates) buying lists and sending emails with your company's domain name in them.
  • Still want to make absolutely sure your campaigns won't get blocked? Consider i-Emailer's new Inbox Inspector tool. It checks the most common spam filters, plus MessageLabs, Postini, and IronPort. You can buy a few of these firewalls yourself and spend thousands of dollars on setup, hosting and maintenance, or just use the Inbox Inspector.
  • Want to continually monitor your reputation? There are services for that (ReturnPath has their SenderScore Reputation Monitor).

Want to find out what your (or your client's) reputation is? Here's one way:

Plug your domain name into this lookup service

They'll tell you if it's on any of the blacklists that they search. If it is, then follow instructions on how to get off their lists (tip: you are guilty until proven innocent, every email you send them will probably be posted on a public forum, and you will be asked for proof of opt-in for each complaining recipient).

Thanks to these big email appliances, it doesn't matter what email service provider or email server you send from, or whether or not your content has spammy words in it. If your name is on these lists, your email won't even get delivered.

Nowadays, it's your email reputation that precedes you.

Other Useful Resources:

  • Free Email Marketing Guide
  • Inbox Inspector: Generate screenshots of your email designs in all the major email programs, test all the major spam filters and email firewalls, and scan for spammy keywords in one click.

Free Email Marketing Tips/Tricks

Sign up for the MonkeyWrench email marketing newsletter. Every month, you'll get free email marketing news, tips, tricks, and advice. See past issues

Email Address:
We respect your privacy.
First Name:
Last Name:

inbox inspector
Will your campaign make it past the spam filters? Check your spam score with i-Emailer's Inbox Inspector tool.
Find out more...

inbox inspector
Do you know if your email's rendering correctly in all the different email programs? i-Emailer's Inbox Inspector generates screenshots of your campaign in 16 different email programs. With one click.
Find out more...