A common strategy for increasing the cost of would-be mail abuse uses a technique called tarpitting. Mail servers that tarpit wait a specified period of time before issuing SMTP responses to the cl...
Updated Jul 01, 2019
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To the best of my knowledge, the fix in 885881 should not influence authentication behavior. I'd check your existing authentication settings to see if a setting didn't take and was enacted when you recycled the service... otherwise I'd use message tracking to see where the message is blocked and drill in from there.