ISP Content Filtering

While ISPs still use IP blacklists to try to keep spam off of their systems, they increasingly use other tactics to keep their users’ inboxes clear of spam while still delivering requested messages.

One commonly used method is content filtering.

This tactic, while designed to help ISPs combat spam, can occasionally affect your permission-based email marketing campaigns too.

Fortunately, with a little understanding about how content filters work, you can reduce the likelihood of them affecting your messages.

What Do Content Filters Do?

Content filters “read” the subject and body of messages to determine whether they are likely to be spam.

When a message is received whose content meets the filters’ criteria for being labeled as spam, that message may be placed in the recipient’s bulk folder. In some cases, it can be bounced back to the sender as undeliverable.

Just like blacklisting, content filtering can result in false positives — email that the recipient has requested and wants, but is treated as if it were spam and not delivered.

Over my next two posts, I’m going to help you minimize your exposure to content filtering, and also give you some tips for dealing with it if it does happen to you.

Reducing Your Risk of Content Filtering

Being able to resolve a filtering issue is important, but it’s a reaction to something that has already occurred.

Before you find yourself in a position where you need to do that, get proactive! Take a few simple steps to minimize the likelihood of content filtering disrupting delivery of your messages.

Verify Your Subscribers.

When your subscribers add to your list, prompt them to confirm that they’ve provided you with the correct address and that the address owner did indeed request your information.

This does several things:

  • It keeps people from getting inadvertently or maliciously added to your list.

    This results in lower complaint rates. Since complaint rates factor into whether a message gets filtered, minimizing your complaint rate translates to minimizing your risk of getting filtered.

  • It keeps invalid email addresses off of your list, which reduces the volume and percentage of undeliverable messages that you send.

    Since undeliverable rates also factor into filtering rules, keeping invalid email addresses from being subscribed to your list will help you to avoid content filtering.

Follow Other Email Best Practices

There are numerous actions and concepts that you can utilize to minimize the likelihood of complaints and content filtering, such as:

  • Set subscriber expectations and build a relationship with them
  • Provide subscriber details in your messages (such as subscribe date, URL and IP address)
  • Send a plain text version along with your HTML messages
  • Thoroughly vet companies before including affiliate or other links to their sites in your messages

While these are certainly not the only steps you can take, they are the building blocks of a filter-friendly opt-in email campaign.

In my next post, I’ll discuss what to do when you do run into a content filtering issue.

UPDATE: the follow-up to this post, how to address false positives, is now available.

10 Comments

  1. Jim Liddane

    9/21/2006 12:00 pm

    As usual, a superb piece of advice.

    I started some years ago using AWeber to send our our weekly bewsletter to songwriters, and I have to say (as I have said before), that if everything on the web was as reliable and as helpful as AWeber – it would be a wonderful internet!

  2. Tim

    9/22/2006 9:35 am

    Justin,
    Great blog!! Over 90% of my sales com from my autoresponder emails. That means without an autoresponder, my sales would be drastically decreased. I’m huge on tracking and testing and have noticed conversions being much lower lately. I blame this mostly on the fact that emails don’t get through and have been wondering what else I could do.

    I honestly didn’t realize how much a factor the undeliverable, subject filter rules would apply. After reading the post here, I’m going to take a closer look at what you suggest.

    Everyone reading this should remember that in truth…the quality of your leads now a days is much more important than the quantity! My combined list of people interested in my wholesale, dropship service is over 20,000 and I bet I could easily delete 30% of them….(the dead weight) and make just as much money. I look forward to the second part of this post!

    Tim

  3. Terry Oster

    9/22/2006 12:25 pm

    nice information, helpful and concise.

  4. Thomas Hunter

    11/17/2006 2:26 pm

    I just started using AWeber to publish my monthly newsletter and I have had an excellent response. Your service is very efficient.

  5. » Easy Way to Remind Subscribers of Their Opt-in - AWeber Blog

    3/6/2007 9:11 am

    […] Among these, you’ll find blog articles on content filtering, a guide to personal e-mail filters, do’s and don’ts for adding subscribers. You’ll also find some important information in exploring our knowledge base. […]

  6. cbread

    10/11/2007 9:52 am

    Everyone reading this should remember that in truth

  7. Best Practices For Bulletproof E-Mail Delivery | Know-How

    10/16/2007 11:01 am

    […] It also keeps invalid email addresses off of your list, which reduces the volume and percentage of undeliverable messages that you send. Since undeliverable rates also factor into filtering rules, keeping invalid email addresses from being subscribed to your list will help you to avoid content filtering. [Source] […]

  8. Best Practices For Bulletproof E-Mail Delivery .

    10/16/2007 1:33 pm

    […] It also keeps invalid email addresses off of your list, which reduces the volume and percentage of undeliverable messages that you send. Since undeliverable rates also factor into filtering rules, keeping invalid email addresses from being subscribed to your list will help you to avoid content filtering. [Source] […]

  9. Sydney Barrows

    8/12/2009 12:32 pm

    So what are the words and other things that set spam filters off? Obviously Free is one of them, but what are the others?

  10. Justin Premick

    8/12/2009 2:44 pm

    Sydney,

    I’m not so sure Free is an "obvious" one – in fact, that’s a common misconception among some marketers.

    Content is still important, and content filters do still exist, but since this article was originally written (in 2007) we’ve seen ISPs move more toward reputation as a means of determining deliverability – in other words, how many complaints are your emails generating?

    As content filters still play some role in deliverability, when you create emails in AWeber, we will automatically check them using a tool called SpamAssassin (a popular content filtering program) and "score" your emails.

    If your email sets off too many red flags and is scored too high, we’ll show you what in your email caused that so that you can change it.