When ticketing is switched on, the hub creates an address such as example-it-support@eml.binaryelements.com through BE Agent Mail. Mail to it becomes a ticket; replies to the ticket's emails continue it; your public replies go out from that address.
Settings › service desk shows the organisation's support address and what to forward to it. Company admins set each company's email domains under Companies, so unknown senders are filed by domain.
Auto-replies and out-of-office mail are dropped and listed under dead letters on the same tab. A reply to a closed ticket opens a new one linked to the old.