I have SSRS 2019 in native-mode with SQL Server 2019 standard behind it. To be very clear, email functionality works and outgoing emails from SSRS is being sent and received. The issue is when the option to attached the report (Include Report) is selected in the subscription options, the following error is received at time of execution:
Failure sending mail: The permissions granted to user '' are insufficient for performing this operation.Mail will not be resent.
I've tried different render format (MHTML, PDF, CSV, XML) to no avail. "Include Link" option works without issue. So unless there is a secret permission somewhere for attachments, I'm a bit confused.
SQL Server Database Mail works and shares the same email configuration values as SSRS.
If anyone has faced this issue, I would love to know what caused it and how you solved it in case my situation is the same.
Nevermind everyone. After I posted my question, I realized the service account was still at the default "Virtual Service Account". After I got an actual domain service account and updated it, plus restarted the service, emails with attachments started flowing through without issue.
Note: I had to delete my 1 existing test subscriptions since it no longer was being recognized with the new service account. After creating a new subscription, there were no more issues with attachment-emails. This in itself could be another problem altogether. More testing is required.