'..Pretty much only Outlook+Exchange do this reliably (for given values of reliably)..'
Just as well you qualified that, @work we've gone from a flaky-as-fuck local exchange server for our primary domain's email¹ to an inconsistent-as-fuck office365 setup..(probably just to tick the 'cloud' box as one of our PHBs is a clueless buzzword believing f.wit).
Personally, I've no use for the Exchange calendar side of things so can't comment on that side of things, I only require it for email, and at least with the old flaky system you stood a fighting chance of getting some of the 'missing' email back, and, yes, email is going missing.
As for Outlook...do.not.want,and.never.have.liked, I've Thunderbird as my main windows desktop email client @work as the least worst available option² talking to office365 via IMAP³.
¹ Just as well we have multiple domains and only he primary domain has been borged into this scheme, the others are still running on 'proper' email servers and not some 'groupware avec email' ones, of course my copy of T-bird is pointed at them as well, and some customers having become aware of the issues we're having with our primary domain, have now got into the habit of firing email to these domains as well as our primary..three copies of orders than none is fine by me.
² I 'Pine' for 'Eudora'...my two main mail clients back in the day, I've just this minute noticed what looks suspiciously like a windows install package for alpine 2.00..I still use alpine on my Linux boxes, so looks like I'll be fecking around with my email@work a bit today....for gits and shiggles.
³ Initially, this worked surprisingly (for Microsoft) well, however, recently I've been having issues along the lines of new emails not showing up in any IMAP client, but being visible in the webmail client at outlook.office365, I'll put it down to shonky code, as I'd hate to think that Microsoft are going back to their old EEE ways again..