Yahoo email with sendmail

[cvoltz]

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:[e-mail]" "I:[e-mail]"
"P:password"
    "R:sbcglobal.net" "M:PLAIN"
    AuthInfo:smtp.sbcglobal.yahoo.com          
    "U:[e-mail]" "I:[e-mail]"
"P:password"
    "R:sbcglobal.net" "M:PLAIN"
    AuthInfo:akadns.net                        
    "U:[e-mail]" "I:[e-mail]"
"P:password"
    "R:sbcglobal.net" "M:PLAIN"
    AuthInfo:yahoo.com                         
    "U:[e-mail]" "I:[e-mail]"
"P:password"
    "R:sbcglobal.net" "M:PLAIN"
    AuthInfo:                                  
    "U:[e-mail]" "I:[e-mail]"
"P:password"
    "R:sbcglobal.net" "M:PLAIN"

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

Thanks,
Christopher