I think the issue here is China's highly restrictive country-wide firewall/censorship policy, rather than unavailability of a particular protocol.
It is a trivial matter for a spammer to trick many SMTP servers into thinking that an email originates within the ISP's circuits though.
Which server software are you using? When not set up a restrictive relay (accessible only by you)? Or a web interface (e.g. Squirrelmail) that enables email to originate from your own server?
I was making a point about how easy it is to use gmail as an outgoing SMTP server, to circumvent all of these issues.
The unavailability (or if you prefer me to say the difficulty in finding accessible servers) of the protocol, and the knowledge required to trick SMTP servers, makes it non-trivial to configure OE or Thunderbird to work within China without using gmail (or other similar SMTP services).
I could set up a web interface, configure a restrictive relay, or even install SMTP server software on the laptop, but why bother when I've got gmail?
FYI, I'm using Sendmail 8.11.7 on Solaris 7 with procmailsanitiser on an old SPARCstation-1 which I borrowed from work 6 years ago. Other than editting the /etc/aliases file occasionally and adding new user accounts, I've not had to do anything to maintain this antique for atleast 3 years