Sharing suppression lists between accounts within your team is useful if you use secondary accounts (those belonging to a top-level account) to manage campaign segregation, but don't want to run the risk of emailing a suppressed contact in one account from another. For example, you might want to do this if you have secondary accounts for each of your offices - so when a contact unsubscribes from one office, another office won't be able to inadvertently contact them again.
Suppressions get shared across all accounts that are opted into the shared suppression feature by the top account, including the top account if they've opted in. For instance, if secondary accounts A, B, C and D are all opted in, then A's suppressions are shared with B, C and D, and B's suppressions are shared with A, C and D, and so on.
Set up shared suppressions
To share suppressions between accounts.
Log into your top-level (parent) account, expand the User menu and select Settings.
Go to Email > Suppression settings.
Under Shared lists, select the checkbox for an account to opt it in to shared suppressions.
Leave the check box clear if you want an account to maintain its own suppression list.
The Share suppressions popover appears.
Select the checkboxes to confirm that you understand:
All suppressed contacts in all selected accounts will be shared among all selected accounts
Unselecting an account will not revert shared suppressions. It will just prevent further synchronisations
After the initial synchronisation, contacts suppressed for a least 24 hours will be synchronised continuously
Any suppressions related to the selected accounts are moved into one suppression list. If the suppression was completed more than 24 hours ago, it’s shared across all accounts that are opted in. However, newer and removed suppressions have a delay of 24 hours, so that you can undo the changes that have been made. If you want to undo the changes, you can delete the suppression under the Suppression history tab. If you want to undo a single suppression, you can resubscribe the contact.
Suppression list synchronisations aren't instant and take place daily across accounts, so allow up to 48 hours for your list to become fully shared.
You can change the accounts that are using the shared list at any time, by returning to Shared lists tab and updating it. As a side note, any new accounts that are added receive any past suppressions.
Once the list is fully shared amongst your selected accounts, the Bounce threshold options will become unavailable for the included secondary accounts. Instead, the bounce thresholds are controlled by the top account, even if the parent account has not opted into the shared suppression list.