How this relates to domain or multidrop mailboxes
A domain or multidrop mailbox is one which receives mail for multiple email addresses (commonly all addresses in a given domain). If you do not want all of this mail to go to one person, you need to know who the messages were originally addressed to after retrieving them from the POP/IMAP multidrop mailbox. You cannot do this by looking at the To:, cc:, or other informational message header fields, because they do not actually reflect the message envelope at the time of delivery. Instead, you have to reconstruct the envelope information from the message header fields which the MTA on the server used to record it at the time of delivery.
If the final MTA does not record the message envelope (the envelope sender, and all envelope recipient addresses in the domain mailbox the message was sent to), then mail will be lost or misdirected regardless of which software you use to access the mailbox. The mailbox cannot actually be said to be a domain mailbox in this case; the defining characteristic of a domain mailbox is that it records the envelope correctly. The configuration of the MTA running on the server needs to be fixed so that the envelope is properly recorded for every message it receives.