How to display <iframe> tag to gmail?

@larissa 

Unfortunately, Gmail does not support the use of the tag for security reasons. This is to prevent malicious code or content from being embedded within emails and potentially causing harm to the recipient's device.

If you want to display content from an external source in your email, you can try using the tag to create a hyperlink to the content instead. This is a safer alternative and will ensure that your email is not flagged as spam or phishing by Gmail's filters.