An alternative is to use some email server from a host/domain registrar/google apps/zoho/etc as secondary MX server. It saves you from having to maintain a second server, and you still get 99% of your messages through your primary server.

I had a similar setup for a while, and it was interesting to see that some messages (spam, mostly) picked the secondary MX by default. Spam servers also seemed to cache the (secondary) MX for much longer than the TTL.