We all are not techies enough to build responsive html content for our marketing mails. There are quite enough good tools to help us. We Corefactors team just wanted to help you to choose the tools than trying to search for it. We have tried and using many of these.
beefree.io – One such good tool to build and download code to use across any email marketing software.
mosaico.io/ – Helps you to build responsive email content rapidly with easy drag and drop and intuitive image upload features.
Stamplia – Create your own email template in minutes with modules. Keep your template design while creating the layout you want. Build, move, destroy, re-build according to your mood. Just like a Lego!
Give a try. all are open source. You will love these tools. Once you design, download the html content and upload in email marketing tool to run your marketing responsively.
Note: Make sure you try sample mails before shooting mass mails.
Thank you developers who developed and made it open source. You guys made our job easy and save money 
