To personalize bulk emails,
In the Bulk email compose window, click on Personalize
Select a specific lead from the list of selected recipients or add new recipients for whom you want to add a personalized message. You can add up to 10 recipients from the Personalize email overlay
Type in the personalized message for this lead
Click Next
In the next screen, you can set up the following:
Give your bulk email a name - for example, Product updates email
Decide whether to send the email immediately or schedule it for a later time
Choose to track the email for opens and clicks
Add an unsubscribe link to make sure your uses have a way to opt-out of your emails
Hit Save (or Send later if you've added a schedule to your email). This sends out the bulk email to the recipients.