When you send an email campaign action through Engage, vega will check for any known invalid emails and will not attempt to send these.
This helps improve your sender reputation and improve your delivery score by not attempting a guaranteed failed attempt.
All emails marked as invalid and not attempted will be added to a list called [Campaign Name] - Invalid Emails. This can be found under Contacts > My Lists.
These emails should be checked for errors and updated where possible to attempt email delivery next time.
Other emails where the domain is discontinued or the correct address is unknown, should be updated so no longer used and another form of contact should be made to get the correct email address.
Here is a list of email addresses flagged as invalid, where % can be any characters:
Includes any of these characters- [ &'''',":;!=\/()<>] (this includes a space)