It appears we are unable to send emails to any Yahoo account, ie, yahoo.com or yahoo.de. Other email providers work just fine Gmail and other corporate addresses.
The emails just sit in queue waiting to send, the only error i can see from Exchange System Manager is "The connection was dropped by the remote host". I have configured rDNS for our domain and it does report back with the correct IP address. I have tested our SMTP and domain using MXToolBox.com and everything is good according to MXToolBox, also, our IPs are not on any black lists for spam.
We are running Exchange 2003 on Server 2003 R2, any help is appreciated.