Is it possible to add/change the "From" field using "mailto:" template? Need to add some default sender email address using this "mailto:"
This is impossible. Link mailto:
opening sofware to send e-mail. User logged in that software is automatically sender.
You can only change other parameters.
Example href:
mailto:person@example.com?subject=The%20subject&body=This%20is%20a%20message%20body