How to send group mail
iPhone has this basic feature to send group mail & SMS Then how to do this
iPhone 5s, iOS 7.1
Per the following, group messages are sent by iMessage if all recipients have iMessage enabled; if not, they are sent as MMS even if they are plain text.
If group messaging isn't in use by the sender and all recipients, then they go as individual SMS messages to the multiple recipients (i.e., not a group message).
Group messaging is turned on/off in Settings/Messages and MMS group messaging requires an appropriate plan from your carrier. http://support.apple.com/kb/HT5760