Sorry for a second post so soon

I'm helping out with the planning for my high school reunion, and we've run into a little stumbling block. We've collected about 170 emails so far, and tried to send an initial email to those people, but have received quite a few rejects due to spam filters.

I'm a little surprised that this occurred, because I wouldn't have figured that 170 was an enormous amount, and I'm pretty sure GMail's own limits are far higher than that.

We would like to use pay services as a last resort, as we have $0 in funds to start with. Does anyone have a suggestion?