I signed up. There's no way to use pop3 or imap.

"OnMail does not have support for using your account with other email applications, such as Apple Mail, Outlook, etc."

https://support.onmail.com/hc/en-us/articles/360048879012-How-do-I-connect-my-OnMail-address-to-a-third-party-email-app-

How do you figure this is awesome?