Hello @KenV19 ,
Would you be able to provide some examples of contacts you know have received the emails before, but have suddenly started bouncing? For security, please reply directly to the automated email from my @ mention.
It's possible that their domain or ISP changed it's security protocols, and has reported to our system that the email addresses are non-existent enough times to trigger suspension. Do you know for a fact that these are still valid email addresses? If so, you may need to reach out to their IT teams (if applicable), and make sure they have your email address safelisted, or our domains safelisted.
It may also be worth reaching out to Deliverability, especially if the number of suspended contacts is more than 10. Deliverability will want to know if a certain domain isn't reporting the proper codes to us for bounced emails, or is causing something that's resulting in valid contact emails being marked for suspension.