What is your mail poll interval (in Outlook)? Have you tried upping it to 10 or 15 minutes? Remember that e-mail is NOT a prattle venue for communication with the instant gratification of instant messaging clients, like Microsoft/Yahoo/Google's IM client. Slamming the mail server at intervals less than 5 minutes apart is abusive and simply wasteful.
If the mail poll interval is too short, any e-mail client that schedules its mail polls will result in aborting the current one to start the next one and this can lead to problems in retrieving e-mails. You could disable the scheduled mail polling in Outlook. Then you would have to manually instigate a mail poll but wait until it completes before you hastily bang on the Send/Receive button again right after the current mail poll completes.
