When your Mixpanel email messages get clipped, your users will have to click a link to see your message in its entirely:
Email clipping is caused by email clients themselves (Gmail, Outlook, etc.) if the HTML file size is too large. For example, Gmail considers any emails with an HTML file size over 102 Kb (which is approximately ~75,000 letters or characters) to be too long.
Preventing clipped messages
Mixpanel itself does not inject email messages with extra HTML, but there are several other reasons why extra HTML might have made its way into your messages and is driving the large file size:
Some browser extensions (for example extensions that check and validate spelling and grammar, such as Grammarly) will inject custom CSS into a text field in order to highlight incorrectly spelled words. If you have the Grammarly extension installed on your browser, disable it on the Mixpanel domain so that your email messages are not accidentally clipped.
If you copy/pasted your content, depending on where you copied and pasted from, you may have unwittingly copied and pasted the HTML as well. Create a new email and actually write out that text rather than copy and paste.
You may simply need to try an Incognito window in Google Chrome or clearing the cache/application data from your browser.
Once you’ve figured out the root cause of the issue, create a brand new email rather than editing the old message, and send a test to ensure the clipping issue has been resolved.