The internal, embedded HTML Editor has basic styling and layout capabilities that allow you to create and edit email templates in a "what you see is what you get" interface. If you would like to design emails outside of this tool in any number of available email-building tools, but send them out of MC Trade's email function, you can use the External HTML Code option.
Go to Communication > Send Email. On the Message tab in the lower right corner, click Use External HTML Code. Click through the message to confirm you want to use the raw HTML option.
Paste in the full code of your email. You can manually enter or update the code in this field.
To preview the email, click "Preview" in the upper right corner. You can also save the email as a draft, and come back to it later with the external HTML option still selected. Finally, on the Send tab you can send a test to yourself or any email to see what your HTML looks like in a rendered email.
Once your email is ready to go, you can send or schedule the email as usual.
NOTE: if you decide you'd like to revert back to using the Internal HTML Editor after using the external HTML option, you may do so, however if you have entered code that the editor is incapable of rendering into the editable, WYSIWYG view, there may be unexpected layout or style changes.