"550 This is not an open relay, Goodbye. [RCPT_TO]"
This is not an Exchange NDR. So for whatever reason the wrong host is being used for delivery. Have you used any other site to test? Such as mxtoolbox
In this video we show how to create an Address List in Exchange 2013. We show this process by using the Exchange Admin Center.
Log into Exchange Admin Center.: First we need to log into the Exchange Admin Center.
Navigate to the Organization >> Ad…
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online.
The email signature template has been downloaded from: