We have an Exchange 2007 on windows server 2003 ,
There is a problem when sending emails to yahoo.com domain,
If a user try to send email from MS Outlook client it will stuck in the exchange's queue (with error: Last Error: 421 4.4.2 Connection dropped),
But if the same user uses OWA and send an email to the same yahoo account it will go thorough and also will clear the yahoo.com queue and previous emails which were send from outlook will receive their destination at yahoo too.
If the users do a " ipconfig /flushdns" command on their computers before sending the email through outlook client , they will be able to send the email to yahoo.com but after some hours it will stop again,
While there is no problem through OWA>
The users are receiving their IP and DNS information from DHCP on AD, and the DNS is pointing to the same AD server.