In order to personalize the messages you write to that group, you don't write a message but a quick template.

Tools -> Quick Templates -> Create a new Quick Template
Give your QT a name and a handle and enable the option 'Use for new messages/mass mailing'

Now you write the message you want to write as a QT, in order to personalize it, you use some macros. It would look something like this:

Hello %ABToFirstName,

I'm writing this message to check your address, are you still living at %ABToAddr in %ABToCity?

Regards, %FromFName
%Subject="Address check"

You save the QT. (Press OK)

Next thing you start the address book:
Tools -> Address Book
Sel ect the address book group that you want to use as recipients for your message and pick fr om the menu:
File -> Mass mailing using template -> pick the QT that you just wrote
Now each recipient will receive his own personalized message.

Note that your QT needs to have the subject set with a macro, because it has no other way to set it.
Also note that your address book also has the option to send a "New message using quick template", that's a different feature, that way your whole group will receive the same message, with everybody in the To: header and personalized to the first recipient.

I hope this makes things clear.

Happy Xmas.