The business requirement is to use the new font (Antenna-Extra Light) for developing an email template. We have downloaded and imported the particular font in the ACC, but if we try to use the imported fonts in template most of the fonts are working as expected in both email and browser but Antenna-Extra Light is reflected only in the browser not in outlook.
Custom fonts do not work in Outlook. You will need to specify a fallback system font that looks close to your custom font, and this will be used in email clients that do not support custom/web fonts. There's more info on applying web fonts and which email clients support them here - https://www.litmus.com/blog/the-ultimate-guide-to-web-fonts/
If the typography is really super important (like for a brand image), then you could create your headline as an image, however this isn't a great user experience and I would only use it as a last resort.