Currently Being ModeratedDec 24, 2013 7:32 AM (in response to mike from dollars des ormeaux)
There are quite a few group emailing apps available on the App Store, but most will not build group email into the Mail app as you ask. You would have to use their own app to send your email.
Uniquely "MailShot Pro" creates special contacts for your groups, which you can use from the Mail app and tens of thousands of compatible apps to build group email right into them.
MailShot can import entire groups from your address book with a few clicks, and is now used by over 250000 people to send group email.
You can find the app at https://itunes.apple.com/us/app/mailshot-pro-group-email-done/id445996226?ls=1&m t=8, a free version is also available, which can only create a few, smaller groups, but it can be upgraded.
Disclosure: I am the developer of MailShot Pro and may benefit from its sale.