Dear AllI have configured MS Outlook 2003 using SMTP/POP3 in my Exchange 2007 SP1. My POP3 works properly and I can not send mail. The following error occurs:Task '192.168.201.29 - Sending' reported error (0x800CCC67) : ' The server responded: 421 4.3.2 Service not available, closing transmission channel'Here 192.168.201.29 is my CAS/HUB server's IP. My MailBox's IP is 192.168.201.31.Need your help.RgdsBari

is your receive connector configured to allow your client's connection?What address do you have your SMTP settings in Outlook set to use? Are you checking the box that says "smtp server requires authentication" and supplying appropriate credentials?Mike Crowley: MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator

Thankz Mike Crowleyur first ques. solved my problem. Yes I had prob. in my receive connector.Thankz again.Bari