Hi All,
I'm trying to get Modern Authentication working, I've got everything setup on the Azure side, when I click the Authorize button in Veeam, I get the green, token is valid tick. But, when I click the test message button, I get the below error:
Type 'Microsoft.Graph.ServiceException' in Assembly 'Microsoft.Graph.Core, Version=2.0.8.0, Culture=neutral, PublicKeyToken=31*************5' is not marked as serializable.
We have logged Case #07023369 with Veeam support, but I thought I should reach out to you as well.
Our advice is to continue to work with support for such issues. But I see that there was already a solution to this case.
Solution for this case:
The sender mail address belonged to a user without an active Exchange Online license. After changing the sender mail address to a user with an active Exchange Online license sending an email was successfull.