Looking to create a good email template.

Can anyone recommend good external visual editor that can be used to create and import email templates to Zoho Campaigns?

I checked Beefree.io and it generally works but Zoho Campaigns dismiss the responsiveness: when I send the email from Beefree it is responsive, when I import the same HTML to Zoho Campaigns the email becomes non-responsive. 

Would be grateful for any help.

Regards,

Andrey