@pwaring
I use Thunderbird and K9 mail with an account on office 365. Never had any problems.
On thunderbird I needed to install an exchange extension, after that I never needed to do anything special.
This is the best part of office 365, the rest is a steaming pile of shit who makes my life more difficult in ways I'd never have imagined possible. I wonder how many UI architects they employed to then just do the exact opposite they were proposing.