As of this morning, subscriptions that had been running successfully for more than 2 years stopped working. I got the following error:
Failure sending mail: At least one of the From or Sender fields is required, and neither was found.
I went through some forums, which led me to check my SSRS Configuration Settings, specifically the email settings. The sender address is present and the SMTP server is accurate. In fact, I used these same settings to successfully setup another server's SSRS Email Settings after this happened today. I made sure I used full emails in the reports and I do. I went to C:\Program Files\Microsoft SQL Server\MSSQL.2\Reporting Services\ReportServer\rsreportserver.config and checked the <From> tag under the <RSEmailDPConfiguration> tag. It is a full email address. In the <DefaultHostName> tag, I added our AD Domain name.
The Default web site and app pool looked ok, but I am not entirely sure I would recognize any subtle issues.
These was also the mention of resetting encryption keys, but I hesitate to do that until I reset other options.
Any other suggestions?