And again, all alternatives have been discussed here (Google "Mac OS X Mail program" and you get the whole list of alternatives), but without knowing what you're specifically looking for (other than "receive, read and send mail", which ALL email programs do just fine), we really can't go much farther.
All of the aforementioned programs can be set up to be a minimalistic mail program, as you desire. It's now just your personal preference on which one to use.
If you want a more specific mail program feature or are looking for a certain look and feel, please state so and we can then narrow down your options.