I'm using TFS2015.
I made a change to C:\Program Files\Microsoft Team Foundation Server 14.0\Application Tier\TFSJobAgent\Transforms\1033\BuildCompletedEvent.xsl and now I'm no longer getting email alerts. So presumably, an error in my .xsl, but I can't seem to find any documentation on where such errors would get logged to.
I looked in the database at [Tfs_Configuration].[dbo].[tbl_JobHistory] but I see nothing relevant.
Worse, I reverted my changes and I'm still not getting email alerts. Unclear how to figure out what I did wrong and how to fix it.
Figured it out. If there's an XSL transform error, it gets mailed to you as the notification. I had another notification issue which was preventing emails from getting to me at all.