All they have to record is alias->real in a giant table.
They don't need to record what app or service got the alias address, and they explicitly state that they do not record any details about interaction with your service, or any emails that go through the alias. It's an explicit statement in the linked talk.
They don't need to record what app or service got the alias address, and they explicitly state that they do not record any details about interaction with your service, or any emails that go through the alias. It's an explicit statement in the linked talk.