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Subscription Form Issues & Spamhaus

Subscription Form Issues & Spamhaus

Recently, Spamhaus started cracking down on potential "list bombing" activity.

In layman's terms, spammers write scripts to find web pages with forms. Then, they go ahead and start submitting email addresses to unknowing subscribers. In other words, someone goes and opts MY email address into YOUR optin form. While this serves no purpose for the spammer, it can absolutely impact your email reputation. I start getting emails from you, that I never signed up for, so out of frustration, I click the spam button.

Imagine this on a massive scale.

If your web forms don't have appropriate defenses in place, then you are at risk for this type of abuse AND an increased risk of a spamhaus blacklisting. According to some reports, this can reduce delivery rates by as much as 40%.

According to Spamhaus (This is a sample message we recently got after submitting for a client who was impacted):

Problem description

The newsletter service ("Sender Name" ) is using the referenced IP address to send bulk email. Unfortunately, the said newsletter service is not verifying the email address of new subscribers. Due to this, the service can be easily be abused to "listbomb" internet users.

Problem resolution

The newsletter service needs to clean up their email address list. Additionally, it has to ensure that bulk emails are only being sent to recipients who have verifiably subscribed to their bulk email service.

In addition, the newsletter service should take appropriate actions to prevent further abuse of their service:

  1. a) Implementing CAPTCHA to prevent automated subscriptions
  2. b) Implementing Confirmed Opt In (COI) to prevent that abusers can add random email addresses to the newsletter service that are not owned by the subscriber
  3. c) Read the documentation below

Further reading

The referenced links below can give additional information:

Subscription Bombing: COI, CAPTCHA, and the Next Generation of Mail Bombs:


Mailing Lists -vs- Spam Lists:


Confirmed Opt In - A Rose by Any Name:



For over a decade Heather Seitz used email marketing to build successful companies and had to solve the biggest barrier to consistent profitability: deliverability. Today, she is the Co-Founder and CEO of Email Delivered.

For more information on subscription form issues and spamhaus, visit http://www.emaildelivered.com/spamhaus/. Remember to sign up for the FREE Email Delivered Pulse newsletter for articles, tips, and recommended resources for email marketers.

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