Hello,
Are you talking about creating newsletters in Adobe Muse? If yes then it is not possible in muse as this point of time. you can refer to the links below.
Using Adobe Muse to create a simple html email template
https://forums.adobe.com/thread/1246018
You can also vote for the same idea in the link below.
Create Newsletters (formated e-mails) from Adobe Muse
Regards,
Vivek