Message is blocked in “SMTP Delivery to Mailbox” queue if exchange server is added in groups of a child domain in Exchange Server 2019 and 2016

Applies to: Exchange Server 2019Exchange Server 2016


In a Microsoft Exchange Server 2019 or Exchange Server 2016 environment, if the computer account of the exchange server is a member of groups (for example, 29 groups) in a child domain, the messages that are sent to the mailbox are blocked in the “SMTP Delivery to Mailbox” queue.


The authentication token is being trimmed at the time of authentication between EdgeTransport.exe and MSExchangeDelivery.exe. Max length that’s accepted for SMTP command is defined as 4,000. However, in this scenario, the length is more than 4,000. So, at the time of command read, it's reading only 4,000 characters and the rest is getting truncated.


To fix this issue, install one of the following updates:


Learn about the terminology that Microsoft uses to describe software updates.