Hi Amanda,
In my experience, something as simple as an update to Microsoft Outlook can cause these issues. This explains why your email may look great in web based email clients, but not in Outlook. There are some best practices in coding emails that will resolve this and provide consistent results across all clients in even the most complex layouts. If you'd like to send me an example, I'd be more than happy to take a quick look at the code and see if anything stands out - ryanm@pedowitzgroup.com.
Best regards,
Ryan