When you design your HTML email it is key that you test your design in different email clients. Webmail services like Gmail, Hotmail and local clients like Microsoft Outlook, Lotus Notes and Windows Mail display your email quite differently.
All Microsoft email clients use Microsoft Word to render the email even though Microsoft Word is far from ideal to display HTML emails.
Heres an example of an email that clearly has not been tested in Gmail:

At Follow-Up we recommend that you run your custom design through our test engine.
Try our test engine
We test your design in 24 browsers, 19 email clients and also do a spam analysis in 14 spam filters. You get a full report that shows the result plus recommendations on how to improve your design.
We can test your e-mail template now. Contact us here to test your current design today .