SQL Server Reporting Services subscriptions fail to send email

We've recently had reports that some scheduled reports that are emailed out haven't been sent/received, looking at SSRS the error that was showing was:

Failure sending mail: The report server has encountered a configuration error. Mail will not be resent.

It turns out that the active directory account for the owner of the subscription was recently deleted. Re-creating the subscriptions with the owning account setup as an active user resolved the issue, though longer term we're going to move to getting users to manage their own subscriptions so that we don't have to keep track of, and refresh, subscriptions when the person who created them (invariably someone within IT) leaves the business.