What
happens is that whenever a new message is sent to yahoo, it replies
with "try again later" message. e.g. here is a test smtp connection to
one of the yahoo's mx:
# telnet 66.196.97.250 25 Trying 66.196.97.250... Connected to 66.196.97.250. Escape character is '^]'. 421
Message from (a.b.c.d) temporarily deferred - 4.16.50. Please refer to
http://help.yahoo.com/help/us/mail/defer/defer-06.html Connection closed by foreign host.
Now
as you can see, yahoo did not even give us (the ip of a.b.c.d) a chance
to start the smtp session. What it will do is wait for us to try again
later. Our mail servers (or yours on your vps/dedicated server) will try
again later and if yahoo likes the delay long enough, it will let the
server communicate further and deliver the email.
