If we sent mail to an email address andwe receive a hard bounce for that email address the owners notifications are switched off.
A hard bounce means the email address is invalid, there is no email or the users has marked you as spam. If we continue to send mail to this address our mail server can be flagged as being spam and added to a Black List meaning ALL emails will be marked as spam, as you can image we DO NOT want this to happen and take care to make sure our mail servers always have a good reputation.
How do I know?
In the top right when you log into MiStable you can see if there are any failed emails this week, you can also download a history of failed emails by clicking on the Failed Emails link.