Check under which tab (inbox, promotions etc.) your email will fall in your recipients' Gmail box, before starting your mail merge.
Many YAMM users are sending emails to other Gmail users. The Gmail inbox is split into multiple tabs (Primary, Social, Promotions) and best is to appear under the Primary tab.
You can use the following service to check where your email will appear for most Gmail users: https://litmus.com/gmail-tabs
It's very simple to use. The service provides a unique email address you can send an email to (from YAMM). Once you have sent the email, click the button 'I've sent it' and you'll see a report.
Once you've checked your email appears under the correct tab, you can start sending it to all your recipients.