installing mail server on Ubuntu using docker and rainloop

i am setting up a mail server at link: https://mail.devlopersguide.com/ for that i am using dovecot to manage my imap and pop3 protocol and using rainloop as my web mail.

but after setting up i am unable to setup my mail account how can i setup my email account devcot.

i have tried all possible efforts but was unsuccessful.

guide followed from

https://notblog.org/install-mail-server