Inline Styling doesn't work with ActionMailer

I am using SLIM and SASS for email templates and styles in my Rails application.

The email looks great when I view emails in a browser with the app environment set for development, but in a production environment, the email looks different with imprecise styles. The images and headers in the email sent from production were missing inline-style tags, but they looked great during development.

What could be the reasons that could be causing the email style to change in the rails app development environment?

PS: I am NOT using gem for inline css.