Unfortunately, Outlook is one of the most notorious email clients for rendering HTML emails; back in 2003, Microsoft decided it would be better to use Microsoft Word to render emails instead of a web browser (even though browsers were built for that purpose). As a result, a lot of design elements just do not render. The exception here is that Outlook on Mac actually uses Safari to render, so emails are beautiful, and Outlook.com (the new Hotmail.com) is also much better. Luckily only 9% of emails are opened on Outlook.
- Images have issues stretching
- No rounded images or buttons
- No gradients
- No animated GIFs (Coming soon to Outlook 2019)
- No custom fonts
- No video support
- Poor rendering of complex designs
Why do other emails seem fine in Outlook?
Without seeing the original email design, it is hard to tell what it was supposed to look like. If an email opened in Outlook looks reasonably good it could (and likely) is different from what it was intended to look like.
Until Microsoft changes Outlook to use a rendering engine designed for HTML, emails will never look perfect.