A hard bounce can render a person's email address invalid when a mail server tells Marketo that the person's email can't be delivered. A soft bounce means something went wrong in delivering the email to the person; this automatically gets resolved and can sometimes takes days. Both hard and soft bounces consist of multiple categories.
There are 5 person strings in Marketo that are related to troubled email delivery.
After a person reaches email suspended status, there is no way to clear the email suspended checkbox. However, the person will still become mailable 24 hours after the initial suspension.
When a person is marked as email invalid, they can only be reset manually (which we recommend you only do if you know for certain their email is valid) by unchecking the "Email Invalid" box in the Person Info tab of their record.
Follow these steps to create an Email Performance Report, which will generate bounce data.
Spam filters sometimes create hard bounces. These "false-positives" are not an indication of the true validity of the person's email address.