Unfortunately, iframes aren’t currently supported by most email providers and iframes typically don’t work in email. This is because email doesn’t function the same as a web page.
Because an iframe is importing content from another source, there are two main reasons it won't work well in an email:
The "passive" email content doesn't change and isn't "live," so it wouldn't interact well with the content of an iframe, which can change over time.
Because iframes load content from an external website, there are large security concerns. Iframes could easily be used to expose your computer to viruses as soon as you opened an email containing one.
Because of these concerns, most email service providers (Gmail, Yahoo, etc.) won’t allow iframe content in emails and they automatically block it. So when you try to use an iframe in an email and it doesn’t work, it’s actually because of the email provider.