Multiple SMTP domains, POP3 Connector Manager Limbo

My company just purchased two additional email domains. They would like certain users to be able to send email using the new domains.

I know how to add the new SMTP address to the receipt policy and then select the users primary address and all works great. Plus all email is hosted offsite with pop3 mailboxes so there is no MXrecord updates etc…

The problem I am having is with the pop3 connector. Once I change the default smtp account with the new one(s). The users email does not get delivered to their mailboxes via the pop3 connector. I know the mail is removed from the offsite mailbox but I am not seeing were it is going? Its like it is going into limbo. I need help! When the original SMTP account is set back to default, mail (from then new domain) gets delivered fine.

Any ideas?