It's also going to take a hell of a lot longer and cost more than buying an Outlook license. If I was lead on that project, you'd have an uphill battle trying to convince me that spending $100k+ on an email solution unless you can point to specific, serious deficiencies in the existing off the shelf solutions.

Software Engineering is far from a lost art: part of the practice is intelligently making cost-benefit decisions.

The current solution is literally causing problems in space. Space-grade engineering is expensive, but having things go wrong on your already very expensive mission is even more expensive.