Today we are announcing the availability of Cumulative Updates (CUs) for Exchange Server 2016 and Exchange Server 2019. These CUs include fixes for customer reported issues along with all previously ...
Updated Apr 21, 2022
Version 9.0
Blog Post
Hi Nino_Bilic The_Exchange_Team,
We have noticed delays in emails with a large number of recipients (500+) that started appearing after applying CU12 to our 2019 servers.
This also triggers on emails using distribution lists.
When looking at logs from message tracking, the low prio is set once Exchange has expanded enough groups that the recipient count is above 500 (or if the email just have enough recipients as is).
Has anyone seen similar behaviour?
Example:
[MsgRecipCount, 358], [SubRecipCount, 359], [DeliveryLatency, 864.997], [AttachCount, 0], [E2ELatency, 864.999], [DeliveryPriority, Low], [PrioritizationReason, AMS:282230/1048576|ARC:717/500]
Can't find where that 500 ARC limit comes from, does anyone know?
A not so important question but relevant that I have not found any info on, what is the difference between MsgRecipCount and SubRecipCount?
From the same email:
[SlaExclusionReason, AccRecipCountThresholdExceeded]
[TRA, ETRP|ERROR=MaxDataSizeExceeded]
Receive Connectors (MS default values)
Default, MaxRecipientsPerMessage: 5000
All else, MaxRecipientsPerMessage: 200
TransportConfig
MaxRecipientEnvelopeLimit: 5000
Specific mailboxes
RecipientLimit: Unlimited
Other
PriorityQueuingEnabled" value="false
EDIT:
We can see the same ARC 500 limit in older logs as well as the Priority being Low, but the latency was never an issue.
Should DeliveryPriority be affecting the email delivery time when PriorityQueuing is disabled? They feel related but I might be wrong.