Outlook slow opening email

I am using Outlook 2000 with Exchange 5.5. Running Norton AV and Norton Antispam. Outlook performance has suddenly become a problem. It takes 30 seconds to a minute to open an email for the first time. Opening mail that has already been read is instantaneous. The antispam software has been running for over a month. The performance issue started last week. Performance of all other applications is excellent. No other users are experiencing a problem. Any suggestions would be greatly appreciated.