You can save past mail merges as a template using the "Save as a Template" option to the right-side of the mail merge. This will allow you to easily craft a mail merge to a new group of recipient using the same content and schedule you have done in the past. You can also create a mail merge template from scratch by using the blue New Mail Merge Template option under the Mail Merge > Mail Merge Template page. Mail Merge Templates are a Yesware Labs feature.
We've recently launched the ability to share mail merge templates. Team Managers can now share mail merge templates across the team and edit team templates. To do so, click the Mail Merge Templates section of the Mail Merge page. From there, locate the Mail Merge Template you'd like to share and choose "Copy" and select the team you'd like to have access to the template.
Mail Merge and Mail Merge Templates are available on our Team and Enterprise plans.
You can also use the Mail Merge Templates for individual recipients. For users on our Enterprise plan, you can use the "Add to Mail Merge Template" option at the top of the Contact or Lead page in Salesforce to quickly launch the Mail Merge Template page.