Is OnMail a standalone service or will I be able to plug-in multiple accounts?

OnMail is a brand new standalone email service. To manage your OnMail account with multiple email accounts, you can use our OnMail mobile app (available now on iOS and Android.) You can also use our account import system to manage your existing email accounts within OnMail*.

Additionally, you can also use the Edison Mail app client, which supports managing multiple email accounts from different providers all in one place - available on iOS, macOS, and Android.

*Account importing is only available for Personal and Professional plans.