Spam has made email an unreliable mechanism. Witness this case of a lost bid:

There it was in the e-mail spam filter, along with offers to invigorate both your bank account and your sex life: an offer to save the Cobb County schools $250,000. But this message was for real.

School officials are blaming an overeager junk-mail filter for capturing and killing a Kennesaw businessman's bid to provide telephone services to the system. It seems the part of the filter that watches for pornographic material was offended by the use of terms such as "long distance."

I have to check my junk folder (both the corporate server-side one, and the local client-side one) regularly - otherwise, I end up missing quite a bit. This has tragedy of the commons written all over it.