You can add subject added to the mailto command using either one of the following ways. Add ?subject out mailto to the mailto tag.
<a href="mailto:test@example.com?subject=testing out mailto">First Example</a>
We can also add text into the body of the message by adding &body to the end of the tag as shown in the below example.
<a href="mailto:test@example.com?subject=testing out mailto&body=Just testing">Second Example</a>
In addition to body, a user may also type &cc or &bcc to fill out the CC and BCC fields.
<a href="mailto:test@example.com?subject=testing out mailto&body=Just testing&cc=test1@example.com&bcc=test1@example.com">Third
Example</a>