In Marketo when an email is flagged as invalid, the value does not automatically change from True to False if that email is manually corrected in Marketo or when it is corrected in SFDC and synced back to Marketo. To try to account for this, I have set up a smart campaign to identify when the data value changes in the Email Address field and have the flow change the data value in the Email Invalid field to False.
Has anyone else found a better solution to this? Or is this the standard process others have set-up to change the Email Invalid value when an email has been corrected?