Hello @JanisD04 ,
I'd recommend checking out this article that covers what suspended bounces are. In order to protect the delivery rate of both Constant Contact and our customers, there are certain types of email addresses that we do not send to. Among them are email addresses that continually bounce as non-existent. Since repeatedly sending emails to "non-existent" addresses can have a negative impact on sending reputation, Constant Contact suppresses these addresses and marks them as "Suspended" in your email reporting. A contact that any of our customers has tried to send to, that repeatedly bounces back as non-existent from their domain / ISP, will get suspended.
You can attempt unsuspensions in your account for contacts bouncing as suspended. You can also respond to the @ mention email you automatically receive from my reply, or call our general support, to have us attempt an administrative unsuspend of the contacts. If you're needing more than 15 contacts unsuspended administratively, we ask that you call our Deliverability team so they can investigate why so many legitimate email addresses were bouncing as non-existent enough in the past for our system to suspend them.
If you decide to unsuspend an address from within your account, as a follow-up I'd recommend doing a Quicksend of the last email they were supposed to receive. If we receive a report from their domain / ISP about them being 'non-existent' again, then they'll likely be put back into suspension. You can check this by going to the contact's engagement history right after doing the Quicksend. If the non-existent bounce occurs again, then it'd be best to reach out to our Deliverability team to see if they have any additional insight regarding that domain / ISP.
See also:
FAQ: What are suspended bounces?
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William A
Community & Social Media Support