Mailmeteor lets you preview your mail merge before sending emails. This is a great way to make sure everything looks right and avoid any merge failures.
To access the preview, follow these steps:
Select a template
Click on "Preview emails".
Here's how the preview looks like:
From the preview, there are several features you can try:
flip through the spreadsheet rows by clicking on "←" or "→";
edit the template to make last time change;
receive a test email to be sure it looks great on Gmail;
Also, by clicking on the little caret next to the recipient email address ("▼") , you have access to more information about the email being sent, such as if there is some cc/bcc recipients, if tracking is enable, which row on the spreadsheet is being merged, etc.