There are a few reasons why an email may look different from client to client. Some clients, like Microsoft Outlook, add extra spacing after certain HTML tags. For example, Outlook will add space after every </p> tag, so you might want to use a line break (<br>) instead.
Styles can also affect how an email client renders an email. If you use an external or embedded style sheet, there's a good chance that Gmail and other popular clients will ignore the styles. Instead, you should make sure to use inline styles for all tags.
Will not work: <style>h2{color: red;}</style>
Will work: <h2 style="color: red;">Text</h2>
If you need to convert your email to use inline styles, you can use on the these resources:
If you're sure that your HTML and styles are correct, or if you are finding discrepancies with our visual builder, please open a new request with Support.