It's meant as local Mailserver wich is not reachable from the internet (No MX record)
It Receives, and sends mail like a mail client, but has multiuser access nstead of single user access of a mail client
e.g.
I have installed Mail@work
The server is fetching mails via Pop3 from 3 Mail Accounts @ my internetdomain and stores them to 3 local Mailboxes, additionally it receves Mails via Pop 3 from my gmx mail Account and stotres them to another local Mailbox.
All local mailboxes are served locally via IMAP to any local mail client
sending mail from a Mailclient are routet to the approniate SMTP Server @ my internetdomain or to gmx
one of my local Mailaccont is named Digi-Quick (no local or virtual Maildomain applied, becuase specially not permitted by Mail@work if used as local Mailserver)
The local Mailaccount maps to the real Mailadress "info(at)digi-quick.de"