Four E-mail-Blocking Causes and How to Fix Them

Why ISPs block your e-mail or route it to the junk folder might seem like one of life’s great mysteries, but the reasons fall into four simple categories:

  • Technical sending problems
  • Excessive invalid addresses
  • Excessive spam complaints
  • Spammy-looking content

There are other reasons, but these are the most common. And as you can see, they’re not personal. Even better, you can overcome them without restarting your e-mail program from scratch.

First, ID the Problem

Contact the ISPs that block the largest percentage of your e-mail and try to resolve the block or filter. You’ll find this information in the delivery reports your list-sending software generates during and after each send. They show which ISPs blocked your message and why, although the reasons aren’t always specific or accurate.

Once you analyze the reports and pinpoint the problem, go to each ISP’s site and find out how it resolves disputes. You might only have to fill out a form. For more serious problems, you might have to work with the ISP’s postmaster team.

No matter whether you fill out a form, send an e-mail, or talk to someone on the phone, be sure you provide all the information the ISP requests. Check with your IT staff if you’re not sure. If you use an e-mail service provider (ESP), someone on that staff likely will run interference with the ISP for you.

Now, you’re ready to clean up your act.

Problem 1: Technical Sending Problems

These include incorrect message headers, errors in authentication records, and no revere DNS (define). If you use an ESP, turn this problem over to your account rep. If not, your IT staff will have to correct the problems. These can be serious errors, but they are generally easy to correct.

Most technical errors show up during times of change. Your IT staff may have added or removed servers for capacity, you have changed service providers, or sometimes even the ISP has changed what it’s looking for. Quarterly testing of your mailing infrastructure can help prevent these types of problems before they become delivery challenges.

Problem 2: Excessive Invalid Addresses

When you don’t confirm opt-ins or clean your list regularly, you pile up thousands of undeliverable addresses. Repeatedly e-mailing to them is a spammer trademark. When you do it, you behave like a spammer and get treated like one. Here’s the fix:

  • Begin confirming opt-ins. Single opt-in is better than nothing, but confirmation, in which the subscriber has to verify his request, is the best way to weed out typing mistakes or malicious subscribing.
  • Add a program that detects mistakes at registration and forces a correction before completing the request.
  • Practice regular list hygiene. Before your next campaign, run a program to root out all malformed e-mail addresses (e.g.,;,, etc.). Your list software also should pull out any other invalid addresses, such as those for closed or nonexistent mailboxes. Then, schedule regular list-hygiene checkups.

Most invalid address problems should be rooted out in your first or second mailing. Excessive invalid addresses that persist beyond these clearly indicate data hygiene problems.

Problem 3: Excessive Spam Complaints

Spam complaints hurt deliverability two ways: First, you can rack up so many complaints per messages sent that you trigger ISP blocking or filtering. Second, you might be re-mailing complainers because you didn’t remove their addresses from your database.

You must act fast on both issues, because your sender reputation depends on both the number and management of spam complaints. Your reputation, in turn, is the number one factor ISPs consider in blocking or filtering your e-mail.

Spam complaints are not evil. They warn you that something is wrong with your e-mail program, which should lead to actions you can take to correct it. Here’s what you should do:

  • Sign up for feedback loops at ISPs that offer them. You’ll get immediate notice that subscribers clicked the spam button on your message, and you can monitor them or find out who in your company is responsible. This information should be on the ISP’s bulk-e-mail or postmaster pages.
  • Watch for ISPs that add feedback loops. Setting up one or two isn’t enough. Reach out to ISPs where you are having challenges, find out if they offer feedback loops, and learn how you can sign up to receive these valuable data.
  • Remove the spam-complaint address as quickly as possible. Move it to a do-not-e-mail database if you have one. Be sure you don’t re-mail to it.
  • Review your opt-in procedure. Do you set expectations about content, format, and frequency, or are your subscribers left wondering what they are going to get?
  • Review your e-mail content. Does it match the expectations you set? Compare your opt-in promises to the e-mail you send now. Ask yourself, “If I were a new reader, would I want or expect this e-mail?” (Be honest!)

Problem 4: Spammy-looking Content

We all know what spam looks like. So why do so many so-called legitimate e-mailers keep sending messages that have all the hallmarks of classic spam, such as:

  • Vague or aggressive subject lines
  • E-mail address or stranger’s name in the sender line instead of a company or brand name
  • Aggressive language in body copy, along with overuse of exclamation points and misspellings
  • High ratio of images to text, especially one large image
  • Oversized, boldfaced red type
  • Too-frequent messages, often with unwanted or irrelevant content
  • Newsletters that look more like solo offers than reliable information sources

Once you understand both the major reasons ISPs block or filter e-mail and how to fix the problems, you should find that deliverability loses that aura of mystery.

Until next time, keep on deliverin’!

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