What do I do if all emails get forwarded to the postmaster because they "do not have local recipients"?

This message means the email does not contain at least a single recipient in it's "TO:", "CC:", etc header fields that reside in one of the "accepted recipient domains" configured in POPcon.

The error only arises with catch-all style POP3 mailboxes, so first make sure the POP3 mailbox you are downloading from is actually a domain-wide catch-all style mailbox. If it is actually a mailbox that receives email only for a single user instead of a whole domain then you can solve this problem bei just changing the configuration of the mailbox in POPcon to "single user mailbox" and configuring the correct forwarding email address of the user in your exchange that receives the email from this mailbox.

If you are actually downloading mail from a catch-all style mailbox POPcon needs to know which domains you do consider your own, i.e. all the domains that you receive email for. Only these recipients are routed to your exchange server to keep the exchange server from bouncing the other recipients (think of an email with multiple recipients).

You can add your internet domain(s) to POPcon's list of "accepted recipient domains" on the POP3/IMAP configuration page (format: "yourcompany.com", without "@" or "*").

POPcon POP3 properties