While you can design the perfect email newsletter, it can still look less than ideal if there’s a coding incompatibility with any of the major email clients (Outlook, Hotmail or Gmail can be notoriously difficult in that regard). In this instance, it's best to do two things: use an HTML email template builder to design your emails and rigorously test your templates. Ideally, you should use a newsletter tool that provides an automated testing tool for different email clients.