There are many mail merge add-ons for Gmail available, this quick read article will allow you to pick the best mail merge extension.
Gmass is an email marketing plugin for Gmail. Gmass.co offers a great Gmail add-on, however the experience may lack of simplicity and the price is overall quite expensive. A Gmass footer is included by default in the free version of Gmass, which may denature your email campaigns.
Mailmeteor is the best alternative to Gmass. In its free version, Mailmeteor offers twice more free quota than Gmass (100 emails with Mailmeteor vs 50 with Gmass). Also, Mailmeteor has more affordable pricing options, for individuals and companies, which you can find in the table below.
About Gmass privacy: since Gmass requires access to emails you may wonder what happens
with your data. Mailmeteor respects privacy by design: it does not have any access to your emails,
contrary to Gmass which can read, modify or delete your emails.