[jlgaddis]

I manage e-mail servers used by "smaller" government users (individual agencies/offices, municipalities, and counties), schools, businesses and individuals -- those who are typically using a "real" mail client (e.g. Outlook) over web-based mail (although we offer that as well).

I haven't ran any type of extensive usage statistics but from what I see daily plain-text POP3 (i.e. 110/TCP) is overwhelmingly more popular than anything else. STARTTLS (with both POP3 and IMAP4) is a bit behind that, followed by {POP3,IMAP4}-over-TLS (i.e. 99{5,3}/TCP).

This is probably due to a mostly stable user base that doesn't reconfigure or set up new mail clients often. As new mail clients are installed / configured, they typically use "native TLS" (not STARTTLS) but I think this is likely because of the autoconfig/autodiscovery that most mail clients (especially mobile) support nowadays.

We will hopefully be completely doing away with plain-text mail "soon" but it will require a LOT of reconfiguring of mail clients.