[JoshuaJB]

Eh, half the problem is that there are far too many options to maintain, many of them legacy. Smart card authentication has worked great in Edge on Office 365 for years without any plugins at Microsoft, so I imagine your employer has got the wrong box checked somewhere triggering a fall back to ActiveX.

[ska]

   Eh, half the problem is that there are far too many options to maintain

In microsofts case, this is partially self-inflicted, and cultural.

[jdsully]

Enterprises want options. How else are they going to disable solitaire and make work as miserable as possible?

[kop316]

So the smart card authentication works (I can log in), it's using the smart card to encrypt/sign emails.

[JoshuaJB]

Oh, I could certainly see that. I don't recall encryption/signing working very well in the best of cases. If you haven't yet, I'd suggest submitting a bug report (I think there's a button somewhere in the O365 web interface). ActiveX is very deprecated and likely will be removed from Edge as part of the move to Chromium (just my personal speculation - I don't know if that's the official plan).