Not sure much can be done here short of the US Government hijacking the .ml domain altogether via ICANN, which, if even achievable, would probably cause worse side-effects than the leaking of low-grade intelligence to Mali. Probably the best partial mitigation would be to make it a condition of doing business with the military to put a blocker on all emails to .ml domain, and for all partner militaries to do the same. Still won't prevent every instance, but they can probably prevent 80% of the most sensitive emails by doing this for 20% of people who communicate with them.