Sending a html email without white left margin

I need a help about HTML email. Recently I have tried to make a html email to someone as my project thing. I've made up a html template and got image files from a designer. So all I need to do is finding a way to send this html email to other recipients. Here below are the details that I have done so far.

Because I am using a Apple mac mail client program I've found a way with this. Open the html document in Safari then Edit > Select All, Edit > Copy then open up a blank email and paste the contents into it. In this way, everything looked awesome but one problem was there was an white gap on the left margin. Please take a look at an attached image.

So I had to find another way to get rid of this white gap. After some trials, I concluded the problem was caused by Apple mail client program. Because as an experiment I have tried to open and copy other html email newsletter that doesn't have a white gap, and paste it in a blank mail message. The white gap appeared up again even though the original newsletter html email hadn't have it.

Next thing I've tried ThunderBird different mail client program. This one has own feature called insert > HTML. With this feature I could create any html email like a website. It's free and cool, but I still need to prefer using Apple Mail program as a main mail client. It would still be a little tricky to use two mail client program in a mac.

So I am just wondering if there's any way to remove the white gap when using Apple's mail program. Any thoughts or advice will be greatly appreciated.