I'm trying to set up PRTG to use an existing Exchange server as an SMTP relay server for notifications. I've configured all the settings in Setup > System Administration > Notification Delivery, and when I set the SMTP Relay Username and Password to be my own personal Active Directory credentials, I can send a test notification successfully. The log shows "Status sending Email: OK", and I receive the test message.
But I don't want to use my own personal credentials for this, so I'm trying to change the SMTP Relay username and password to another account. No matter what other account I pick for this, the test massage does not get sent, and the log shows "Error sending 'EMail': Client does not have permissions to send as this sender". This tells me that the identity being used to authenticate to the SMTP server do not match the from address of the email. But in the Notification Delivery settings I've changed both the Sender E-Mail and SMTP Realy username fields to match, so where is the mismatch occurring? Do I have a hidden configuration somewhere that is using my personal email address as the "From" address, so that's the only one that works?