So, when a SQL Server Reporting Services subscription gives you an error message like: "Failure sending mail: The report server has encountered a configuration error. Mail will not be resent." You know exactly what to do to fix it right? Just fix the so called "configuration error". Problem solved! Another day another dollar. Am I right? Unfortunately, "configuration error" is sufficiently vague that it could be anything. In my specific case it turned out to be caused by a subscription being "owned" by a user account which had been disabled.
Use the query below to find your failed subscription and take a look at the username column. Is that account disabled? If so you can use our world renowned change the owner of an SSRS subscription script to set things right.
USE ReportServer go SELECT d.SubscriptionID ,e.name AS ReportName ,e.path AS ReportPath ,d.LastStatus ,d.LastRunTime ,u.UserName FROM dbo.Subscriptions d JOIN dbo.Users AS u ON d.ownerid = u.UserID JOIN dbo.Catalog e ON itemid = report_oid WHERE d.LastStatus = 'Failure sending mail: The report server has encountered a configuration error. Mail will not be resent.'