Stupid Question
 

If I install sendmail 8.12 will it overwrite the sendmail 8.8.7 that I already have installed or will I then have two versions of sendmail installed?

If you install to the exact same directories then you will overwrite the previous version. If you install to different dirs then you could end up with two different versions. This is most liekly if your current sendmail is the original one with your distro and hasn't been installed with its default settings, then you build sendmail from source using the default settings.

cheers

Jamie...