I would but it's restricted here at work, and I wanted to see if my home mailserver backup was actually configured correctly

Anyone know of a website that will let you test a SECONDARY mail server?  I want to find out if it is allowing my email in.

 Thanks

http://www.dnsreport.com/ does some very basic tests. But not about whether emails to you would be accepted/forwarded. You'd better find out yourself by sending test emails from external accounts (when your primary MX is down) or having someone sending you an email.

Use the ip address of the secondary to telnet to port 25 and enter the smtp commands by hand and see if it is delivered.

Is it an MX service or do you control it yourself? I've had trouble in the past finding out from MX backup hosts what blacklists and policies they use. IMO a poor MX backup is worse than having none at all - they either are just a conduit for spam, or they let nothing through at all.