While I haven't added a lot of features to reMail since then, I've been trying to keep it up-to-date and buildable. The changes that happened in iOS 5.0 and XCode 4.2 broke the build a while ago, and a variety of downloadable zip files sprung up with forks of reMail that build on iOS 5.x.
The good news is that I just pushed a patch that builds reMail on iOS 5.x flawlessly. Many thanks to Matt Ronge who put this patch together. He helped a lot with reMail even back in the day: reMail uses the MailCore framework he built.