如何在单元格中创建图像填充HTML电子邮件的整个高度？

I've got a problem with an HTML email in that if the content is is increased the images that make up the left and right hand side are too short so it leaves a gap. I don't want to just make the images longer as this could leave lot of whitespace depending on content. I had the idea of using the same image twice with one set to I've got a problem with an HTML email in that i