After using above Fastmail server settings for Fastmail and on other email applications, you’ll be able to set up or synchronize your Fastmail on other email apps. Hope this content, solves your Fastmail settings issue for Fastmail. If you need specific help and support to configuring your email app, then you can contact Fastmail Support Help Service help and manufacturer of the third-party email application.
https://www.emailhelpdesk.us/support-for-fastmail.html