I am still not understanding.
The server I am setting up will host multiple different domains for email, yet the users table is only going to have the hostname of the server for all users? For example, it will have
user1@example1.com and
user2@example2.com
resulting in two entries in the users table but since the server hostname is example1.com, user2 will also have example1.com in the mail_host field. It would help to know what roundcube is using this field for.