Is it possible to perform a reverse DNS lookup in a stored procedure or from a SQL Server Agent job?

You can use a simple technique that relies on xp_cmdshell to perform a reverse DNS lookup. Xp_cmdshell can be a security risk if not managed properly, but it can also be a powerful tool for doing specialized tasks in a controlled manner from T-SQL. For example, you can use the following code, then manipulate the output any way you need to.

DECLARE @OSCmd varchar(8000)                              DECLARE @DomainName varchar(8000)                              SET @DomainName  = ''                              SET @OSCmd = 'NSLOOKUP ' + @DomainName                              EXEC master.dbo.xp_cmdshell @OSCmd