When Marketo identifies a bounced email, it should be able to update the 'Email Bounced' function in Salesforce. This article link provides a workaround, but bypasses the standard field in Salesforce. The field may not be available to the API yet, but why not update the standard Salesforce field?
I created a Smart Campaign to deal with this situation and I was able to update both the standard Salesforce fields. My campaign triggered whenever Email Invalid was changed to True and updated both Email Bounced Reason and Date. Also, I filtered out any emails that were already marked as bounces (Email Bounced Date is empty) from running through the campaign.
Here's the exact campaign:
Smart List(Use ALL Filters)
Data Value Changes - Email Invalid - New Value is True
Email Bounced Date is Empty (want to exclude any email address that have already been flagged in SFDC)
Flow (Lead Can Run Through Everytime)
Change Data Value - Email Bounced Date - New Value is {{system.dateTime}}
Change Data Value - Email Bounced Reason - New Value is Marketo Bounce
The SFDC Confirm Email Address flag (the yellow caution triangle) will appear next to the email address if it has both a Bounced Date and Reason.
Also, we've trained our reps to fix the email address in the SFDC by clicking on that caution triangle. Therefore, I set up a second campaign to update Email Invalid to false if the email address is corrected:
Smart List(Use ALL Filters)
Data Value Changes - Email Address - New Value is Not Empty
Email Invalid is True
Flow (Lead Can Run Through Everytime)
Change Data Value - Email Invalid - New Value is False