There are a few group email apps out there but the best solution is probably MailShot. This creates special groups as single contacts in your addressbook that you can email, just like the feature was built into your phone.
You can then use them from within any app to send to your group, and can do a few tricks like forwarding emails to your groups which you cant do with any other method.
Free for a limited version, the paid upgrade lets you email up to 50 people at once!
There's a functional workaround to send Group emails that takes some setup, and a copy-paste. But it's easier than any one-by-one solution cooked up without a 3rd-party app. Here's the way:
Go to Settings>General>Keyboard-->Shortcuts
Add a new Shortcut by typing in the full email addresses in the "Phrase" field, separated by comma and space; type in the few letters representing this "Phrase" in the "Shortcut" field.
In the email app, IN THE BODY OF THE EMAIL, type in the letters for the Shortcut and space. Then Highlight-->Copy this text and paste it into the To: Field. (Obviously: Delete this text in email body; and use CC: or BCC: fields as desired.)
Regrettably, you CANNOT just type the Shortcut in the address fields as it gets lobbed into one address.
This "No Group Email Functionality" rates a #FAIL by Apple. One of the few.