Emails not going through, ExplicitlyDiscarded, HADISCARD
https://social.technet.microsoft.com/Forums/en-US/236a7eeb-9d6b-4747-9ffd-f00d54917337/emails-not-going-through-explicitlydiscarded-hadiscard?forum=exchangesvrsecuremessaging
Office365
Get-InboundConnector
Get-outboundConnector
Get-ReceiveConnector
Identity Bindings Enabled
-------- -------- -------
NL-EXMBX01\Default NL-EXMBX01 {0.0.0.0:2525, [::]:2525} True
NL-EXMBX01\Client Proxy NL-EXMBX01 {[::]:465, 0.0.0.0:465} True
NL-EXMBX01\Default Frontend NL-EXMBX01 {[::]:25, 0.0.0.0:25} True
NL-EXMBX01\Outbound Proxy Frontend NL-EXMBX01 {[::]:717, 0.0.0.0:717} True
NL-EXMBX01\Client Frontend NL-EXMBX01 {[::]:587, 0.0.0.0:587} True
Get-ReceiveConnector -id "NL-EXMBX01\Default Frontend NL-EXMBX01"|fl max*
MaxInboundConnection : 5000
MaxInboundConnectionPerSource : 20
MaxInboundConnectionPercentagePerSource : 2
MaxHeaderSize : 256 KB (262,144 bytes)
MaxHopCount : 60
MaxLocalHopCount : 12
MaxLogonFailures : 3
MaxMessageSize : 36 MB (37,748,736 bytes)
MaxProtocolErrors : 5
MaxRecipientsPerMessage : 200
MaxAcknowledgementDelay : 00:00:30
Customized receive connectors limited to 20 messages from 1 source at a time, increased to 200
Set-ReceiveConnector -identity nameofconnector -MaxInboundConnectionPerSource 200