An Email merge template must already have been setup by your Administrator on Setup an Email Merge Template.
How to run an Email Merge
1. Select Contacts from the Object Navbar.
2. Click on Tools > Mass Action button from the Action bar. Mass Action dialog opens.
3. Select a Record Source. There are 4 options: Selected Records, All Records from Account, Public Mailing List and View.
a. For Record Source = Selected Record. Email recipient are the selected contacts, count of which is displayed on screen.
(Note: This option will only show if customer has selected records from the open view) 
b. For Record Source = All Records from Account. Email recipient are contacts under the selected Account.
On the Accounts dropdown, select an Account.
c. For Record Source = Public Mailing List. Email recipient are contacts with the same entry on the Mailing list field.
On the Public Mailing List dropdown, select a Mailing List.
d. For Record Source = View. Email recipient are contacts listed on the selected view. Here is a link on How to Create a view.
On the View dropdown, select a View.
4. Set Exclude from Mailing List checkbox as needed.
5. Select Sender
6. Select Reply To
7. On the Email template dropdown, select a Template.
8. Select Delivery Priority as needed.
9. Select Importance as needed.
10. Type Internal Comments as needed.
Notice that Mail Preview displays. This shows the number of recipients and other details.
11. Click Proceed.
12. Click Yes to confirm action.
- E-mail is sent and activity log is created.
- This Email then goes on a queue and will be sent in a set interval by a CRON process