In order to use UNION, the column list for all the SELECTS must be the same (at least in type/length), since it's returning a single resultset; you're basically trying to return both the email and the ...

I’ve created a script that monitors a table in a SQL Server database. I’m only interested in one column in the table: TimeStamp. If the maximum (newest) value in TimeStamp is more than 30 minutes ...