DNS settings for Google Apps:

1) Set the following MX record for your domain .

domain.com. IN MX 10 aspmx.l.google.com.
domain.com. IN MX 20 alt1.aspmx.l.google.com.
domain.com. IN MX 5 alt2.aspmx.l.google.com.
domain.com. IN MX 10 alt3.aspmx.l.google.com.
domain.com. IN MX 10 aspmx2.googlemail.com.
domain.com. IN MX 10 aspmx3.googlemail.com.

2) Then set the CNAME record for your mail.domain.com

Replace mail entry from

mail IN CNAME domain.com
to
mail IN CNAME ghs.google.com

If all the setting is correct and then it will take 1-2 hours to update at word wide . After that you can access your google mail by using the URL http://mail.yourdomain.com(external link)

Note: Replace yourdomain.com equal to your original domain name.