ISP Feedback

The emails you send are often at risk of landing in the spam folder, or worse, blacklisting the sender. See how ISPs work to make sure you’re avoiding common mistakes, and learn how to improve your list’s health. 


  1. The role of ISPs on the email deliverability
  2. Blacklisting
  3. Analyze the bounce rate & spam traps
  4. How to improve the health of your database?

1. The role of ISPs on the email deliverability

ISP is responsible for the biggest part of the delivery process. As the effect of an accelerating increase of email traffic, ISPs are introducing more and more advanced filters which makes it even harder to earn the place in the customer’s inbox, such as:

  • sending limits limiting the option of sending emails, based on the number and/or weight of the message, 
  • email bulking – sending emails to the junk or spam folder by default,
  • blacklisting – email sent from a blacklisted server or domain doesn’t stand a chance to land in the recipient’s inbox,
  • blocks – occurs after receiving too many spam complaints or having too many hard bounces

2. Blacklisting

In the topic of blacklisting, ISPs have the possibility of choosing their blacklisting tools. There are two types:

  • ISP custom spam filters evaluate the collected information with spam points for each instance of wrong behavior,
  • public Blacklists work in cooperation with many ISPs with whom they exchange information about senders. The benefit to the ISP is that it does not pass spam on to its users, while the blacklist benefits by receiving more feedback on spam that has been reported by ISP users.

If the spam score gets too high, the emails will immediately land in the trash folder or even be bounced back to the sender.

3. Analyze the bounce rate & spam traps

Sending the email doesn’t mean that it would land in the customer’s inbox successfully. There is always a possibility of a message bouncing back. The bounce rate indicator can be divided into 2 types:

  • hard bounces – permanent delivery failures, for example when email doesn’t exist, it’s invalid, or server doesn’t exist,
  • soft bounces – temporary deliverability failures, such as a full inbox, too large email file, sudden increase in sending volume, or too high frequency for engagement levels.

Spam trap is an old, recycled email created by ISPs or public blacklist providers which isn’t actively used by a real person. It is used in order to detect email senders that try to send emails to not verified, inactive users. Each sender has to make sure that the spam traps are not present in their mailing list, in other cases it can heavily decrease their reputation.

4. How to improve the health of your database?

Here’s what you can do to keep your email lists healthy:

  • use double opt-in
  • give the recipients a way to resign from your emails, 
  • adjust the frequency of campaigns to the customer’s engagement, 
  • don’t use unverified emails lists (spam traps risk), 
  • automatically remove hard bouncing addresses from your list, 
  • use feedback loops to block users marking your messages as spam. 
If you need more information about the topic mentioned above, please contact us: +1 800 960 0640