After creating a mail domain and mailbox (as described here: Getting Started with VPS)
You can download the settings from the ISPManager panel, in the section "Accounts → Mail domains → Settings "
Cautions! as a username, you must specify the full name - along with the domain
As an imap/smtp/pop3 server, you specify the address or IP received when the server was issued, or the one you specified when editing the MX record of the domain in the [DNS] panel (https://fornex.com/help/dns/):