I have 1 email address sales@whatever.com. 2 of my salespeople need access to this email account to download orders and reply to customers. Both people work from different locations in the building. My problem is both computers have to be in sync with each other, so if one person replies to an order the other person knows about it. What's the best email client and how so I set it up.

Your best bet would be to use an Exchange account with Outlook.