I am in the process of migration Exchange 2010 to 2016 server. Currently I have installed Exchange 2016 which is co-existing with 2010. I have created a test mailbox on the 2016 server.
I am able to send e-mails to the test 2016 mailbox from 2010 mailboxes both internal and from public.
However I cannot send any e-mails from the 2016 mailboxes to the existing 2010 mailboxes and also to any public e-mail.
E-mails from 2016 to 2010 are being stuck in the queue