Configure access to the internet Roundcube

[helioh3]

I currently have a Ubuntu Server 04.16 LTS running a mail server: iRedMail + Roundcube. Can internally access the e-mail server: meu_ip / mail locally ... as set up external access to that server so that the user type: mail.meudominio.com.br and can access the e-mails.

Any help is welcome