Disable Mail.app's data detectors

Why you’d want to do this I can’t fathom – the data detectors are probably the best feature in Mail – but you can turn off the little pop-up windows that appear when you hover over dates, addresses, and contacts in the application. Go to your terminal and type:

defaults write com.apple.mail DisableDataDetectors YES

Then restart Mail. You should be a happier, if spiritually poorer, person.