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?
Hope all that makes sense.