Thank you for reaching out to the community, that is a great question!
Repeatedly sending emails to Non-existent email addresses can have a negative impact your deliverability rate and your sender reputation. Therefore Constant Contact has put a safety in place to prevent any negative impact on your sending reputation. Suspended email addresses are known to have bounced repeatedly from the Constant Contact system and are now blocked by the mentioned system. For more information about suspended email addresses please visit this FAQ article.
If you would like someone to look into this for you and possibly remove these email addresses from the suspended list, please contact our support team by phone. We will be glad to assist you further!
Please let us know if there is anything else we can do for you.