poor decision making skills
Make software to do one thing well, and to be easily used with other software. That's the kind of software it is smart to choose. Choosing software that tries to be all things to all people is choosing inflexible software that will be increasingly difficult to use in a rapidly-changing world, choosing to lock oneself into a single tool so that it's very difficult to migrate away even when it's doing more harm than good, and choosing to chain oneself to unnecessary complexity.
Email applications should not be different from anything else, in this respect, but these applications should be the same in that they should be tools that each do one thing well and play well with others -- not piles of feces that each do a million things poorly and are actively hostile to all other software in the same environment.
