What’s the best way to export/import suppression lists?

Suppression list transfer is critical. Failing to import suppressions means emailing people who bounced, unsubscribed, or complained, damaging your reputation immediately.

What to export:

Hard bounces: Invalid addresses that will bounce again

Unsubscribes: People who opted out (legally required to honor)

Complaints: People who marked you as spam

Soft bounces: Addresses with persistent delivery issues

Manual suppressions: Any addresses you've blocked for other reasons

Export process:

Most ESPs provide suppression export in account settings or via API

Export as CSV or JSON with email addresses and suppression reason

Include timestamps if available

Verify export is complete (compare counts)

Import process:

Import to new ESP before sending any email

Verify suppression categories map correctly

Confirm import completed successfully

Test that suppressed addresses are actually blocked

Ongoing sync:

During parallel operation, sync suppressions between ESPs

New bounces/unsubscribes on old ESP should suppress on new ESP

Automate if possible via API integration

This is the list of ships banned from port. Letting them dock anyway gets you flagged by harbor authorities.