Contact Pruning helps you automate the process of keeping the most engaged contacts on your lists and excluding the oldest, least engaged contacts from your future sending.
When Contact Pruning is enabled, contacts are automatically blocked after a specified number of emails are sent with 0 opens.
The Contact Pruning setting is on your Settings Screen under the Sending tab.
Set a limit on the number of emails that can be sent to a contact without any opens.
Contact that goes over this limit is then set to a "Stale" status in the account.
"Stale" contacts will be suppressed from receiving non-transactional email. Transactional email can still be sent to Stale contacts.
To send to contacts that have opted into transactional email only, you must:
A) HTTP API - Pass the parameter "isTransactional = true"
B) SMTP Relay - Add a header "IsTransactional" with the value of "True"