I found an answer to my problem. Scoured the net this afternoon again, changing my search terms around a bit and stumbled on this handy little site, and from it I was able to figure out that there were a few lines in my sendmail.mc file that had to be adjusted, and most importantly the hosts file had to be changed so that it wasn't just looking locally. Here's a link to the site where I gathered my information:
Hope this link will help other people. It IS possible to get sendmail going using Dynamic DNS, it's just tricky.