Well - don't.
Using other people's work is very important on the road to any success. When you build some software from source (tarball), you miss the opportunity to use the distro's package manager's work.
You won't get "free" updates. Most of the time none ever updates the packages they installed from source. Because they need to track the software for new versions, rebuild it and all the dependent programs (try to remember them).
You will have problems with other packages from your distribution's repos. This is exactly the case stated in the question: ubuntu has a great package manager and some very nice people maintaining the packages. And they have decided, that for the mailx program to work you need an MTA. So if you installed postfix from sources ubuntu wouldn't ask you to install exim.
If for some reason the maintenance of the server passes to some other person (e.g. your project becomes very successful and you decide to hire another guy to manager the servers while you are busy with other stuff) he will naturally expect to run
dpkg --get-selections to get all the installed packages.
Try to use the distro's package management software as much as possible. Learn to build your own packages if you can't find one prebuilt and you'll become a better professional.