Is it possible to send HTML code in a letter?

Question

PHP

It means not to send a letter in HTML format, but for example to send such a thing:
Please insert this code on the page of your site:

<iframe width="560" height="315" 
src="https://www.youtube.com/embed/jUiutK1gwCY" frameborder="0" allowfullscreen></iframe>

Or is it without a chance and the mail services will cut it anyway and the best thing to do is to give a link to the page for obtaining such a code?

Answer 1

$html = '<iframe width="560" height="315" src="https://www.youtube.com/embed/jUiutK1gwCY" frameborder="0" allowfullscreen></iframe>';

htmlspecialchars( $html );

PS The first thing that came to mind.