You have a very good point there; I actually use Thunderbird at work, using client-certificate authentication like you say. However, I thought my smallish comp

You have a very good point there; I actually use Thunderbird at work, using client-certificate authentication like you say. However, I thought my smallish company was just weird that way. And it doesn't seem like many companies are willing to move away from Microsoft office tools; the FOSS community has been pushing Open/LibreOffice, Thunderbird, etc. for probably 20 years now, with very little uptake. I can see how Mozilla might have finally gotten tired of it. Also, the big problem with Thunderbird is (correct me if I'm wrong) it doesn't do any calendaring (I don't see it at my company), which is the "killer feature" that Outlook has. Google does it with GMail, and it works great, and it's really necessary if you're going to try to get anyone to switch from Outlook/Exchange. But FOSS has never done a very good job of coming up with a drop-in replacement for that.