You can re-configure your spam settings to not flag the messages as spam, they might be too strict if they are detecting spam in messages that aren't spam. Whitelisting is also an option, but honestly configuring your spam settings so that your server is properly detecting spam vs not-spam would fix most of the administration that would come with having to put in whitelist entries or trusted sender entries.
Matt Petty
Senior Software Developer
SmarterTools Inc.
www.smartertools.com