Sending a letter to customers with an email address

I want to send a letter to my customers who have email addresses.

I have the letter saved as a template under "Letter" menu in the card file window.

If I select the template it opens in Word with the Mail Merge option but I do not know how to get it to mail merge with MYOB card file.

I have previously sent a letter using this template but I cannot remember how i did it.  Please help urgently?

Thank you