Whilst throttling is available, it seems to be across what ever comes through the spool, even for the hosted domain (so internal emails get throttled too). Our situation was that today MS flagged us with 'temporarily rate limited due to IP reputation." Whilst I have been able to get the filter lifted a little, the company are still sending lots of legitimate emails across a wide range of MS accounts.

So question / idea, is to allow outbound throttling again certain domains, such as outlook.com / msn / hotmail / live / whoever etc so that I can limit those to X number of emails per hour. But non-throttled domains carry on as normal.