Hi,Recently i have installed an Exchange Server 2007 and all the role (Mailbox, CAS, and Hub Transport) installed on one server. All the mails route from Exchange to Smart Host (Upstream Organisation).Everything is working fine. Only when some users send an email outside of the organisation to more than one recipient(Group of users), the message will be in the queue for a long time. The error message in Queue next to the message i get is: "421 4.4.2 connection dropped". The complete error i get is under Last Error in Queue.....451 4.4.0 Primary Target Ip address responded with:"421 4.4.2 connection dropped." Attempted failover to alternate host, but that did not succeed.Either there are no alternate hosts,or delivery failed to all alternate host.After one day the message will be sent. also when i restarted the exchange 2007 then i did not get any message in RemoteSMTPConnector Queue.Does anyone assist me why this is happening? Please.....

I've seen this happen before when the sending server's ip, or the ISP's entire subnet get placed on a block list. You may want to investigate this. You can start here: http://openrbl.org/client/ You will also want to enable the smtp protocol log and view the log file for additional connection details.