I reaching out i the hope someone came across this issue or could shed some light.
We are using an OnPrem Exchange 2010 SP3 in a hybrid setup.
The issue suddenly occurred. All messages from one cloud user to internal or external recipients are rejected. The sample mail flow is like when I send from o365 to Internet, it should first go to the on-prem, then on-prem send it to internet.
But the messages seems to be rejected from the on-prem everytime. Actually we don't want to re-configure the hybrid wizard because other users have no issue. Only this specific user has this issue. I have also tested on the OWA from other machine and
it can be reproduced. It seems that on-prem server only rejects that sender.
Here is the error
#550 5.7.10 The e-mail account does not exist at the organization this message was sent to. Check the e-mail address before re-sending. ##
Here is the connection encryption message
Message sent to webmail.mydoimain.com at <myIP> using TLS1.0 with AES256