If you just paste ''Mail to: xyz@example.com'' into an email message, the vast majority of email clients will render the email address as a live clickable link - though it won't appear as clickable in Thunderbird's compose window. Save it as a draft or cc it to yourself to see how it appears to your correspondents. If you really need or want the formal mailto: syntax, compose in HTML format and use '''Insert|Link''' and enter: mailto:xyz@example.com Note that this forum's software recognized the mailto: bit and presents it as a live clickable link. Or you could enter it using something like: <a href="mailto:xyz@example.com">Mail to: xyz@example.com</a> so in your correspondents' email client, it would look like this: [mailto:xyz@example.com Mail to: xyz@example.com] Again, you may not see the final result in the Compose window.