What version of Outlook are you using? Do you mean that take a long time after you hit send to come back to Outlook or users say they aren't getting the message? I would suggest putting it in cached mode.
Mark Morowczynski|MCSE 2003:Messaging, Security|MCITP: Enterprise Support|MCTS:Windows Mobile Admin|Security+|http://almostdailytech.com
Would you please provide more detailed information regarding the issue?
1. How the Outlook connects to Mail Server? Mapi or POP3/SMTP?
2. How do you know the Outlok takes a long time to deliver the message? Whether the recipient takes a long time to receive the message or your get an Outlook Send/Receive Progress window when clicking Send/Receive button?