I have two new installed exchange 2019 (SVR01 & SVR02) servers coexisted with Exchnage 2013. I sent an email from a user mailbox to a shared mailbox both hosted on SVR01. however when analysing the header, the following happens:
SVR01 send a request to SVR02
SVR02 send a respond back to SVR01
Why would SVR01 (the host of two parties) send a query to SVR02 when it's got the mailboxes?
Hey there! Are the messages received in the end or does an NDR with the "possible mail loop" get generated?
Have you ran the Get-MessageTrackingLog to analyze the SMTP flow for this specific email a bit more in depth? It could either be that the send/receive connectors are wrongly configured. Or this could simply just be the Shadow redundancy that is causing "issues"
But I would suggest looking into Get-MessageTrackingLog to find out a bit more, feel free to post the results here and we can look into it a bit more together :)