Can't say either way, but after spending a few minutes Googling S/MIME support, it seems completely incompatible with most web browsers and web email services. The only exception appears to be Office 365 with Internet Explorer on Windows? While end-to-end encryption of emails is nice, I'm not sure the benefits outweigh the drawbacks, unless required by regulation. It'd be nice if more webmail providers and browser makers supported S/MIME, especially considering new privacy rules in the EU...