Best practice: Access to users email when they are out of office?

We have a small sales department that uses Outlook Express for their email clients. We have a group policy that locks computers after 10 minutes of inactivity.

Problem: When a sales person is out and another sales person needs to check their email (incoming sales messages), what is the best way to handle this?

Obviously, I don’t want employees trading passwords. Right now my solution is to temporarily change the password to the employees who is checking it.

Any better ideas?