Fedora Users — Yahoo email with sendmail

Can someone please post a working sendmail.mc and a corresponding authinfo file for an account which can send email (via sendmail) using Yahoo's email servers? I am setting up a friend's machine to send his mail through the Yahoo email servers (he has Yahoo DSL) but despite trying various solutions listed on the 'net, email still doesn't make it through. The email appears to be accepted by Yahoo but then it bounces back or gets a DSN: Service unavailable error message (depending on the sendmail settings).

Relevant entries in sendmail.mc are:

define(`SMART_HOST',`[smtp.sbcglobal.yahoo.com]')dnl FEATURE(`authinfo',`hash /etc/mail/authinfo')dnl define(`confAUTH_OPTIONS', `A')dnl define(`confDONT_EXPAND_CNAMES', `True')dnl TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl

Authinfo looks like this:

AuthInfo:smtp.sbc.mail.yahoo4.akadns.net "U:username@xxxxxxxxxxxxx" "I:username@xxxxxxxxxxxxx" "P:password" "R:sbcglobal.net" "M:PLAIN" AuthInfo:smtp.sbcglobal.yahoo.com "U:username@xxxxxxxxxxxxx" "I:username@xxxxxxxxxxxxx" "P:password" "R:sbcglobal.net" "M:PLAIN" AuthInfo:akadns.net "U:username@xxxxxxxxxxxxx" "I:username@xxxxxxxxxxxxx" "P:password" "R:sbcglobal.net" "M:PLAIN" AuthInfo:yahoo.com "U:username@xxxxxxxxxxxxx" "I:username@xxxxxxxxxxxxx" "P:password" "R:sbcglobal.net" "M:PLAIN" AuthInfo: "U:username@xxxxxxxxxxxxx" "I:username@xxxxxxxxxxxxx" "P:password" "R:sbcglobal.net" "M:PLAIN"

where username and password have been changed to protect the innocent.

Thanks,
Christopher