MassMailer lets you add the merge fields in the email templates. You can do this for a regular email content or even to the URLs that are embedded in the template.
If you are using the MassMailer Template Builder, go the respective email template and select the specific merge field that you want to add in the URL for example, {!CampaignMember.Name}
You can add the URL merge fields to the Text URL, Button URL, Image URL, HTML Block URL, or a Video URL.
The following pictures depict the same on how you can enter the merge field in the URLs.
Select the merge field and copy the merge field text.
TEXT URL
Enter the Text Block and highlight the text that you want to link as URL and enter the URL as shown below.
BUTTON URL
You can enter the button content item and edit its URL property as shown below.
IMAGE URL
You can enter the Image content item and edit its URL property as shown below.
HTML BLOCK URL
You can enter the HTML clock content item and edit the HTML to add <a href="enter the URL with the merge field"> tag with the merge filed.
<div class="our-class"> <a href="mydomain.com?contact=">I'm URL with Merge Field.</a> </div>
VIDEO URL
You can enter the Video content item and edit its URL property as shown below.