That would be preferable to what happened to me once. I tried using a + filter and it was accepted but I never received booking information for my trip. When my trip was getting closer I realized I didn't have a confirmation number, and after a long conversation with customer service, it turned out that instead of "<email>+<filter>@gmail.com" my email address was saved as "<email> <filter>@gmail.com", so nothing ever made it through to me.

I'll bet that's a URL-decoding bug -- space gets encoded as plus, so if they decoded an extra time your plus would turn into a space. I've made that mistake a few times myself.