What happened to Mail Merge?
Mail Merge is now called Sequences!
You can find Sequences by hovering over the Mixmax "M" in the top right corner of Gmail and selecting Sequences:
Or click Sequences in the left column in the Mixmax web app:
Why the name change from Mail Merge to Sequences? You can now reuse a mail merge by adding new recipients. And you can add recipients one-by-one — not just via CSV upload. (Click a mail merge campaign you sent in the past to open it up, and click the New Recipients tab. You'll see a spot where you can add new rows to your spreadsheet of recipient, or upload a new CSV.) You can think of this feature as a reusable series of emails, rather than an email that's you're sending to multiple recipients.
You can read all about Sequences here: Sequences Overview