*ahem*I would like to point out the following obvious (in retrospect) advice about testing smtp auth by hand:
when using mmencode to translate to base64, one should printf "username" | mmencode not echo "username" | mmencodeOf course, it wasn't working from my usual MUA either, originally; but after I fixed my problem, I didn't know it was fixed because I was testing with a bad username and password.
*sigh* After a complete deinstall/reinstall/reconfigure didn't work, I caught on...