If a member's email address has been marked as invalid, but the member says that it is a valid email address, you can re-mark the email address as valid. What that will do is to allow emails to be sent to those email addresses again. However, if we receive a permanent failure response again, they will be re-marked as invalid.
From Admin home, go to the individual member's page in the admin panel. In the email section (left hand column), click on the link Mark as Valid.
Click here to find out how to get a list of all members' email addresses that are invalid.
Click here to find out why an email address has been marked as invalid