We are now scanning imported email addresses

When you import a list of contacts, we now scan the email addresses checking for validation and deliverability. If the email address is detected to be invalid and undeliverable, the contact's subscribe status will be changed from "Subscribed" to "Undeliverable" and emails will not go out to that contact. If you feel this setting has been changed incorrectly, you can manually change the Undeliverable setting to Subscribed.

This feature is designed to decrease and prevent bounce emails, which helps to maintain the sender's email reputation and avoid getting flagged as spam.