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.