In Apple’s Mail.app, when you right click on an email address and choose “Copy Address”, Apple decided that you would inexplicably also want the name part, so the string copied looks like this:
Hilton Lipschitz <firstname.lastname@example.org>
I have yet to find a single occasion when I wanted anything but the email address part.
To correct this issue, jump into a terminal session and use:
defaults write com.apple.mail AddressesIncludeNameOnPasteboard -bool NO
Quit and restart Mail.app. Copy an email address and you get an email address:
This is one of those simple annoyances on OS X that I wish Apple would just change the default by default.