How do you monitor for outbound SMTP problems w/o a data center?

Good Morning, Once upon a time we had I had a data center that could monitor if SMTP was working by just running a test message routinely. My hardware moved and monitoring moved back to me. I am looking for solution to notify me after hours if SMTP is failing. I run a multi server enviorment complete with blackberry, so if a system is down a diffrent once can send me an email and I can get it. My idea is to create an agent that generates an email to an outside test account about every 15 min durring non work hours. I would run a seprate agent on a diffrent server to check my mail.box’s on the SMTP server to see if more then 1 of these messages are pending, then notify me if that is the case. Any one know if this is already created by some briliant develper (humble admin here)?

I know there have to be other solutions out there. What do you do to monitor this?

Thanks in advance

Laura