We recently ran into a problem with SSRS where our email subscriptions were processing, but no emails were going out.
SSRS doesn’t really give you any info in the web interface to give you any clue that something isn’t work right, let alone help you figure out what the problem is.
I was able to solve the problem by looking at the various log files that SSRS creates: ReportServerWebApp__X, ReportServerService__X, and ReportServer__X.
In these config files I was able to find some errors coming back from our mail server.
This lead me to discover that the problem was with how the email addresses were formatted.
The issue was that we recently changed which mail server we used for sending out these emails, and we have moved from an Exchange 2003 server to an Exchange 2007 server.
Exchange 2003 would accept domain accounts as destinations for emails, so you could send an email to “cmay” and it would be delivered. It seems that Exchange 2007 requires that you provide the full email address: email@example.com.
After changing some of the SPs that served up the data, all worked once again.