This app can send a mass mail for the group individually. Because you can put inside address or addressee info for the each mail, you can pretend as if you are sending mails one by one.
 
One mail will be translated into 100 mails for 100 people. You don't need to set a bunch of addresses to To:, CC:, or BCC:. You don’t need to worry about others seeing who received the email by To: or CC:. Addressee will receive personalized email.
 
Good for the following scenarios:-
・Announcing farewell party, wedding party, reunion, etc.
・Customer messages.
・News letter.
・Greeting mails like X’mas mail, etc.
 
Feature
・Group edit
　You can edit "Contacts" group. Group mail will be sent for the group. (Even Exchange base contacts like GMail, you can edit the group. (only on your device))
・Variable for mail subject and body
　{firstname:}　→　first name
　{lastname:}　→　lastname
　{nickname:}　→　nickname
　{prefix:}　→　prefix
　{suffix:}　→　suffix
　{company:}　→　company name
　{name:}　→　display name same as your device's "Contacts" list
　Variables above will be translated to your "Contacts" info.
・Individual group mail send
・Background sending
・Keep sent history
・Attaching a photo (from your "Photo")
・Attaching a file from Dropbox
・Multiple sender account
　Password will be saved only on your device by safe way "Keychain" apple provided.
・Designated domain search
　Multiple backword search for your email addresses. You can save the words. If you put company domains for the search, the app will find all of email addresses on your "Contacts" and send mails for them. You can search email addresses too.

Manual
http://iphone.suakx.com/Individual_Group_Mail_Sender/manual

For iOS6 user
You cannot use this app without accessing your "Contacts" data. If you denied accessing "Contacts" already, please set it on at
Setting > Privacy > Individual Group Mail Sender

Attention.
You can send emails via SMTP server only.
Mails will be sent by UTF8 and BASE64 encoding.
(Addressee needs understanding the encoding.)
Sending mass mail in one time, you might get penalty from the mail server.
(Sending 500 over emails per day at gmail, you cannot send any mails for a day, for example.)
Please note the above before purchasing.