We recently had an angry reply to a mailigen email campaign. He claimed he has "unsubscribed 5x" but was still receiving emails. Not sure if he unsubscribed correctly.
The real problem with the integration is that a coworker previously removed his contact info from pipedrive. I used our synced contact list in mailigen and apparently his contact info was still in there. So removed contacts in pipedrive are not removed on the synced list.
I've since gone in to unsubscribe the email manually in mailigen.