Bugbear & Msexchange 5.5

Recently, my server has been infected with Bugbear and as result, I think, the IMS service of the Msexchange stopped sending e-mails however it continues to receive. The server has NT4 SVR with SP6a and Exchange 5.5 with SP3. Virus protection has been accomplished using McAfee with recent updates. And the IE5.5 was updated with SP2.
Do you think that I should remove Exchange and reinstall it again?
What do you suggest?

Thanks