The reason for this is that some versions of Outlook have certain security settings that filter out:
Background images.
The transparency of buttons (Box Opacity).
Overlaying images or elements on top of other images or elements. This includes text boxes, images, videos, or buttons.
Here are our top tips that you can follow to make sure your emails look as good as the rest of your referral program.
Instead of using a background image in your campaign, we suggest making the background a solid color. The fewer elements in your emails, the smaller the chances of the styling breaking.
Avoid adding images and videos to your email notifications so that it's less likely that Outlook's security settings will interfere with your emails.
Don't add buttons to your email notifications. They have a certain % of opacity and Outlook's security settings will remove the button and break the styling.
Something to keep in mind is that not all of your users will experience this problem, for two reasons:
1. Not everyone uses Outlook. Gmail and Apple mail are very common email providers so this will not affect everyone.
2. This styling issue only occurs in certain versions of Outlook. This will depend entirely on the version of Outlook being used and the security settings of that version.