The high mobile data cost was because said developer lives in the arse end of the middle of nowhere, and he refuses to use Mercurial properly (does a full hg clone instead of hg pull every time he contributes, drives me bonkers to be honest but the man writes good code!)
Said developer also admitted, publicly, to using an unlicenced copy of VS Enterprise after a disk crash. That was an indefensible state of affairs to me, and so the only thing I could do without wasting scads of time was to buy him a licence.
Please don't conflate HERMES Mail with Mail/X. They have similar user interfaces and are mail clients formerly written by different developers at the same company, but they are in different languages, different devs as stated before, and target different platforms.