These are the points you should remember when creating an HTML email

Developers always recommend simple structures and attributes for the sake of compatibility with HTML mail because an email page doesn't support everything that a browser's web supports just like external CSS and frameworks like Bootstrap, and Tailwind. So there are certain restrictions or points that you should always keep in mind while creating an HTML email.

Don't use any API's CDN links because it won't work here. Infect if you want to use icons, so use an icon image instead of the <i></i> element. Fonts can be used by importing them into CSS like @import URL instead of the HTML tag <link/>.

For styling only use inline CSS, as external won't work here but in internal CSS you can create media queries or some basic styling for universal selectors.

Use table structure instead of <div/>.

You must test the email first by sending it to you. You can consider these free HTML email testers or senders but remember that they all have testing limitations, so use them properly. Postdrop, Litmus-PutsMail, MailNinja-Previewer