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:
