Hi @SMartinSJC,
This works in some HubSpot tools but not consistently in others. I’d always recommend testing this from different devices (for example, custom mail to links in marketing emails don’t work on certain devices ).
From a first glance in the CTA tool, it seems to work fine:
Testing the CTA, it opens my email client and populates the fields correctly.
This is the generator I used: https://mailtolinkgenerator.com/
Hope this helps!