Everyone likes to point and laugh, sure, I'm getting a chuckle as well. However, on more practical level, what are other options? Outlook, the desktop application works really well with local copies, is pretty low bandwidth and very familiar to end users. IMAP with Thunderbird is probably only other option that would satisfy the requirements. EDIT: Yes they need to get email in space. It's easy way to send documents…
IMAP probably not so much, It depends too much on having a good network. unless the imap server is on the spaceship(heh, spaceSHIP, that is an optimistic term, but it is all we have, so going with it), I would not expect it to work all that well.
I am not very familiar with outlooks game, Historically my beef with with it and thunderbird was their local data store, I mean it was not strictly speaking bad, but I was like "we have this great Maildir spec, why are you using this propriety database that is prone to corruption, even if you don't like Maildir million files approach at least use sqlite"