3 Common Definitions of Email Filters

Understanding the technical definitions of bounced, blocked or filtered isn’t as important as determining the the underlying cause of these delivery issues. What do they mean and how do you prevent them?

Here are the top three common definitions that you will find and how to avoid them:


  • Non-Existent Address: Also known as “hard-bounces.” These are address that do not exist or have been cancelled. Check for: typing errors, ensure that if a company address is used that the owner of the address hasn’t left the company, many free services will also deactivate accounts after three months.
  • Undeliverable E-mails: Also known as “soft-bounces.” These are email addresses that cannot be delivered because the receiving server is unavailable, overloaded or could not be found. Sometimes these problems correct themselves and the emails are successfully sent in subsequent mailings.
  • Mailbox Full: This indicates that the email was not accepted because the recipients email box was over the storage limit. If over a period of time you continue to receive the same message it is safe to assume that the account has been abandoned or the use does not check their email frequently.


  • Block-Lists: These contain lists of domains or IP addresses of known or suspected spammers. If a sender is on the list, its emails likely will be blocked. If you know you are on the block-list contact the ISP or block-list owner and work with that party directly to solve the problem. Two popular block-lists are: SpamCop and SpamHaus.


  • A method of sorting emails – ISPs filter emails based on their content. Filtered email is not returned to the sender, instead it is moved to a folder other than the inbox. This usually occurs when on a per email basis and is typically used by corporate networks and ISPs.

Making sure that your emails are delivered at the highest rate possible is a matter of paying attention to not only email content but also the error messages received and finding the best way to avoid them ensuring that your customers receive your newsletter or email.