We have a free responsive email template with different elements, modules, and supports the new email editor. PM me and I will send you the link of the zip file. That should be good to get you started.
Are you editing the email or editing the email template? Marketo has pre-defined editable regions and you have to go into the template to change those. The new email editor has several templates that are responsive out of the box.
At this point, every single template we offer as a Marketo Starter Template is responsive by default on different versions of outlook and mobile. (they actually always were, but I won't bore you with the details about that )
I will explain a few things you may run into:
-If you need to modify the structure of a module (i.e. remove an element from the module or add an element to a module), it's quite simple but it must be done in the template's HTML. If you're not comfortable enough doing that, we have a great services team and LaunchPoint partners that can assist you.
-The templates are built to handle common use cases...you'll always have simple "modules" available for insertion like free text, free image, 2 column, separator, footer, header, etc... so that you can build out your email. Again, if you require something different/custom the code must be modified.
-If you utilize the color options, spacing options, text editor, and modules, it's generally possible to build an email the way you want it to look. I've had a few customers ask me to show them an example and they were surprised that I was able to get the email looking identical to their mockup from their design team in <5 mins. I definitely recommend you look through the docs so you understand all the formatting options available in the editor and how they work.
-Until the Q3 release, there is a product limitation that requires you to pick an image that is either identical size or very similar size to the placeholder image in the template. If you pick something completely different, you will see bad results in certain email clients.
-Also until the Q3 release, any of the "variables" you edit on the right-hand pane are global in scope. This means that if you modify the value of the variable and it is also used elsewhere, it will change the value everywhere in the email. This isn't ideal if you have two copies of the same module. We are introducing module-level variables in the Q3 release and will be updating our Marketo Starter Templates to use these.