Client is asking why 4 emails have been delivered to 4 contacts who all have same address.
Test1: tested with 2 contacts and didn't use A/B testing.
Outcome: was told would be delivered to ~1 address and was only 1 delivered - GOOD
Test2: tested with same 2 contacts with A/B - 50% to A and 50% to B (so no FINAL mailing)
Outcome: was told would be delivered to ~1 address and was only 1 delivered (to A mailing) - GOOD
Test3: tested with 4 contacts sharing same email with A/B - 25% to A and 25% to B and 50% to FINAL
Outcome: was told would be delivered to ~1 address. Had 1 delivered (to A mailing), 1 delivered to B mailing, and 1 delivered to Final mailing - BAD
So I think A/B testing is causing 'dedupe by email' to break