Mass Emailing in Lightning allows you to send an email template (Complete with images, merge fields and attachments), to a list of contacts, person accounts or leads. This feature was referred to as “Mass Emails” in the Classic user interface, but is now known as “List Emails” in the Lightning experience.
Steps:
Create your Contact/Lead/Person Account List View. Use the filter feature to drill down to the exact recipients you want to receive your email.
Next, check the box in the list view next to each name of recipient
Find the List view button (featured in the image above)
Compose your own email content or select a pre-built email template (also add merge fields & attachments)
Once your template is complete, review your content to preview your email before it goes out.
Hit Send!
There are some limitations to consider with this feature:
List emails can contain up to 32,000 characters.
You can manually select up to 200 contacts or leads from a contact or lead list view.
List emails count against an org’s daily list email send limit, which is typically 5,000 emails per day. This limit doesn't include individual emails you send.