Outlook isn't the fucking problem, exchange and its bastardised architecture is.
To this day I cannot fathom why companies would ever roll out a proprietary exchange setup when there are better solutions available, at a significantly lower cost. Solutions that are more reliable, more secure and better supported cross platform.
Get a router supporting DD-WRT and add custom route configurations to put all non VoD / Gaming traffic or anything requiring all of your bandwidth through a VPN like Vyper or something. That sufficiently covers most browsing / text communications. TBH I wouldn't bet that the security services don't have the power to snoop into encrypted / VPN connections on our national infrastructure anyway, but why would you care as long as you're not a terrorist or kiddie fiddler? You just want to prevent Theresa May and her bullshit short sighted policies from snooping on you for no justified / legal reason (like they probably already have been, anyway).
+++ and a lot later than you would expect from the so called pioneers of recent web browser technologies. They've only just caught up with other vendors, I have no idea what the fuck Apple's management are doing bearing in mind that Safari is literally WebKit with some additional integrations.
Don't believe me? Look at the revision history and release cycle, it's insulting.