Again abhiz you have posted this wiki page on a topic that it has no real relation to...
xtops the command
should show you the responses your server got back from the Yahoo servers. You should see lines like the following
grep yahoo /var/log/mail.log | grep status
If you see lines like this in your log then the Yahoo servers are accepting your mail. What is likely going on is after accepting your mail the Yahoo server is marking it as spam and putting it in the users Spam folder.
Oct 6 09:13:20 email postfix/smtp: 1EF56904001: to=<firstname.lastname@example.org>, relay=127.0.0.1[127.0.0.1]:10024, delay=0.44, delays=0.03/0/0/0.41, dsn=2.0.0, status=sent (250 2.0.0 Ok, id=03526-11, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 1111A111111)
Oct 6 09:24:02 email postfix/smtp: 1111A111111: to=<email@example.com>, relay=b.mx.mail.yahoo.com[126.96.36.199]:25, delay=642, delays=0.01/0/640/2.5, dsn=2.0.0, status=sent (250 ok dirdel)