I need help creating a custom responsive html email newsletter

Hi,

I've created this simple html code in photoshop by exporting the html and images from a spliced and hyperlinked photoshop design. I've uploaded the linked images to imgur, as I wasn't sure if there was a better way to host the related images.

I have managed to copy the html into a gmail email and get the code working, but the problem is that the images in the email aren't responsive to the varying screen sizes that the email is viewed on.

Would you be able to help me adapt the code to make it work responsively across all different platforms and screen sizes? I also would like a simple way to send these emails without editing the gmail code each time that I send an email, so would also appreciate any ideas on how to make this process simpler.

Thanks,
James