Hello Axel,
Thank you for reaching out to us.
We suggest you stick with the web-safe fonts from the plugin customizer options as most email clients don’t allow other fonts. You can read more about font support in emails here: https://www.litmus.com/blog/the-ultimate-guide-to-web-fonts/.
On the other hand, if you want to use Tahoma within the Email Designer, go to Custom Styles, add this CSS code and replace the font-family with the one you want to use:
#template_header h1,
#template_header .subtitle,
#body_content_inner,
.td,
.text,
#template_body h2,
#template_body h2 a,
#template_body h3,
#template_footer a.ft-social-link,
#template_footer #credit { font-family: "Tahoma", sans-serif!important; }
Hope this helps and let us know if we can assist you further.
Regards,
Karla