How can I add icon?

How can I add a mugshot icon to all my emails?

When a a recipient receives an email from you, it is the responsibility of the email client software to display an associated icon. The icon/image isn’t actually part of the email.

If you have a Gravatar account associated with your email, that icon will be displayed. If you have your own domain, and your email is on that domain, you can establish a series of favorite icons in the root of the web site for your domain:

android-chrome-192x192.png
android-chrome-512x512.png
apple-touch-icon.png
favicon-16x16.png
favicon-32x32.png
favicon.ico

This covers various bases for different email clients, as well as other uses. An email client will then attempt to obtain the icon associated with your email by fetching it from the domain (and caching it).

Not all email clients do this. I imagine most of them these days do, but it is up to the email client. Em Client does work in this regard, but still, it’s your responsibility to make an icon (or icons) available for use and the email client software’s responsibility to actually use it.

More info here:

https://support.emclient.com/index.php?/Knowledgebase/Article/View/180/5/how-do-i-change-my-own-email-account-avatar

Does this apply to Windows 10 on a laptop please?

Yes. It’s a concept that’s not associated with a particular operating system.