When an email bounces multiple times it will eventually wind up on your suppression list, to ensure that you do not keep attempting to send to non existing emails that will wind up hurting your sender reputation.
Receiving mailservers use the way a sender handles bounce messages to evaluate the quality of the sender. If the sender does not remove defective e-mail addresses this may result in future e-mail from the same sender being seen as spam and marked as such.
To make sure you avoid being seen as a spammer it is very important to remove defective e-mail addresses from your list. The Heysender webhooks and suppression list will help you with this.
Remove email address from suppression list
Should an email address be on your suppression list by accident. Maybe a recipient has had a full inbox while you were trying to send them an email. Then you can remove the address from your suppression list quite easily. Log into your Heysender account and navigate to Domains, now click the sender domain where it the address it listed on. Now click on the suppressions tab. Locate the email address that you wish to remove from the list, and simply click the trash can icon on the right hand side.
Now you are able to send emails to the recipient again.