1. Install Mail Merge add-on to Thunderbird.
2. Create E-mail Contact List in MS Excel as shown below and save it as CSV (Comma delimited).
3. Create a new message for Thunderbird file menu and enter {{email}} instated of email ID in "to" field and "{{firstname}} {{lastname}} , " instated firstname and lastname of the receiver person.
4. After completing the 3rd step just click Mail Merge option for file menu after a dialog box is open, select source as CSV, Deliver mode as [Send later, Send now, Save As Draft] I selected Save as Draft, Format as [plain text, HTML, Both] I select Both and keep remain all default as shown in above image and click OK button and it result as follows.
Enjoy :)
Source: https://addons.mozilla.org/en-US/thunderbird/addon/mail-merge/