Instructions to identify possible invalid email addresses and to set them to Marketing Suspended while you manually clean them up. In this example, Marketo hasn't marked them automatically as Email Invalid yet. Alternatively you can skip setting the records to Marketing Suspended and simply use a Smart List to review and fix the records.
Create a batch campaign to set suspected invalid email addresses to Marketing Suspended.
Email Address contains
In the flow besides setting the Marketing Suspended field to True, I am going to set a custom field called 'Marketing Suspended Reason' to 'Set Marketing Suspended to True due to possible invalid email address.'
As I mentioned earlier, you can also skip setting a batch campaign and simply use a Smart List to review and fix the records.
Note: I am unaware of natively being able to fix email addresses in Marketo in an automated fashion. For now it's only a dream.