The best thing I've seen is a service that receives your mail before it ever gets to you, filters it for all kinds of bad things and then you pull the (clean) mail from them.
Costs money - YES. Effective - Yes Plus you get reports and you can view and/or release any mail that was flagged and held back from you.
You would be amazed at the type of things going on inside companies and their email: dirty talk between employees having affairs, dirty jokes, not to mention spam and virus-laden emails.
If you don't want to do it at the domain level, you have to invest in something that runs on the desktop and plugs into the email client to filter it as it's pulled into Outlook.
The benefit of something like MXLogic (which I have used), is that the spam/virus laden emails NEVER get into your system.