“Sending has been suspended…”

I’ve gotten an email from MailPoet (“pausedsending@mailpoet.com”) saying that “10% of my emails sent recently were rejected by the recipients” and that sending has been temporarily suspended. However, when I looked through the subscribers list, none of the email addresses were invalid and there were no bounces. I haven’t imported any subscribers and don’t know why there’s a problem. (I have two websites and checked them both, and both subscriber lists are clean.)

I’m not sure what needs to be done next. Has anyone else had this issue and was able to resolve it?

Thanks in advance!