There are plenty of email users on IMAP, and they use web mail to host mail storage. The IMAP clients can do S/MIME (or PGP I suppose).

The bigger problem is trustworthy user discovery service i.e. a directory to exchange public keys. This exists at an enterprise level (active directory) but not globally.

Usually anyone that buys into the viability of PGP email will also tell me with a straight face that the MIT keyserver is completely appropriate for civilians.

Hi jaggs, I work in Gmail. Yes a lot of lurk on HN. I don't understand your "Send as" flow. Are you sending email to some 3rd party owned account? Usually that sends as SMTP MSA (login/password), so that should work. Is it broken when someone replies?

Also posting the email headers with the appropriate anonymization helps a lot too.