Send emails automatically to a list of contacts with specific attachment
You may want to play with standard MacOS X tool - Automator.
Not a big expert myself :), but I know it helps in exactly this type of tasks.
Here are couple of useful basic tutorials on Automator: 


http://www.macosxautomation.com/automator/learn.html
https://www.youtube.com/watch?v=Z56PBanBSx4