Sometimes when you are in OS X and you copy and paste an EMail address from Mail.app you get something like:
Jeffrey Jackson <firstname.lastname@example.org>
You only wanted the email address, not this. We can fix that. Close Mail and open Terminal.
defaults write com.apple.mail AddressesIncludeNameOnPasteboard -bool NO
Now open mail and try again you should just get the email address:
Now go email someone.