Okay, so I just sent out an e-mail to 18 or so people - principals, teachers, guidance counselors - asking them for registration forms for some workshops that the foundation is holding in September. One of them bounced, and included in the long string of machine-generated technobabble explaining why and how it bounced was this:

X-Spam-Report: Spam detection software, running on the system "mf2-3", has
identified this incoming email as possible spam. The original message
has been attached to this so you can view it (if it isn't spam) or label
similar future email.

So apparently, my e-mail was mistaken for spam. Heh... whoops.