If an email is not sent because the address is on your Global Block list then that error should be clearly stated. Currently it just says "not delivered" which causes wasted time on the users part tracking down the problem.
Thanks for sharing this feedback! We understand that the term "not delivered" can be confusing so we're working on getting that changed in the near future. Only some of the non-existent bounces will actually end up being globally blocked because of their bouncing history but I understand the need for clarification.
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