I currently have two accounts on Protonmail - one personal and one for business - but I'm getting fairly annoyed at some longstanding bugs in their mobile client and I'm looking to switch. I also want to use Yubikeys (something PM has long promised but still hasn't delivered).

I found pages saying Zoho supports Yubikey for authentication, but I have two questions I can't find the answer to:

1. Can multiple Yubikeys be tied to the same email account? Such as a primary one and a backup one?

2. Can the same Yubikey be used for more than one email account? I wanna maintain separate accounts for business and personal use.     Edit : want to use the same key as 2FA for both of them