The eComm templates most of us use are 600 pixels wide. So, if you insert an image wider than that into your email, it’s going to throw off the formatting—maybe with weird-looking white space on either side of your header or maybe with misalignment of other content in your email. Avoid these issues by resizing your images to 600px before uploading them—or even smaller if you’re using them alongside text.

Jot “600px” on a post-it and stick it to your monitor for quick reference!