Hi Meredith,
This is something we've been working through recently, so hopefully I can provide some insight to what I've found -- especially since it isn't very clear in Marketo.
There are 3 types of hard bounces that Marketo registers:
-
Email Incorrect - this email address doesn't exist - email invalid is set to true
-
Anti-Spam Block - Marketo suspends sending of emails to this address for 24 hours - email suspended is set to true
-
Technical Issues - email bounced for an unknown reason, can attempt resend immediately
Email Invalid means that the email address doesn't exist (whether due to email, or domain), and Marketo will never attempt to email to that address again.
There's more information in this discussion:
Need more detailed information about email bounces which was where I found this information.