I've seen it now allows to select a client certificate for exchange accounts, however, that option disappears if 'Manual' is selected to specify the server or other settings, which is my case since autodiscovery is disabled.
I don't kbow if the certificate settings are preserved in the Manual mode or not, I'd suggest adding them there for settings clarity.
The client certificate is mandatory in my corporate office365 account, but I've not been able to authenticate with aquamail. The outlook app works with the same certificate, but its garbage compared to aquamail.