Windows Server SBS 2011, running Exchange Server 2010:

Our client has their own Exchange e-mail accounts, but also some old POP3 accounts which are hosted somewhere else but are still in use. So we use the POP3 Connector to pick up those e-mails and deliver them to the correct mailbox. One of these mailboxes is throwing errors at us:

One or more (2) e-mail messages in the POP3 mailbox account '(...)' on the POP3 server '(...)' have invalid header fields. Because of this, the messages cannot be delivered to the Exchange Server mailbox '(...)' in Windows Small Business Server. The messages are still on the POP3 server. To resolve this issue, connect to the POP3 mailbox account, and then manually retrieve or delete the messages.

So I did as the error message said, I logged into this POP account with Outlook and deleted the 2 e-mails. However I still keep getting these error messages. All the Exchange and POP3 services have been restarted, the POP3 connector log has been cleared, the server has even already been rebooted but this message keeps popping up every 5 minutes. So it looks like the POP3 connector is trying to pick-up e-mails that don't even exist anymore... Any way to get rid of this error message, or even better: fix the issue? Thanks.


After a reboot the POP3 connector couldn't really still try to access the emails that are deleted. Either deleting them didn't work (are you sure you accessed the right mailbox? Might be a different one this time) or they are still in some sort of local cache. It could be a local POP3 proxy server - anything like that active in your system?

In any case you might want to check out a 3rd party POP3 connector that doesn't have any of the annoying problems of the built-in POP3 connector: POPcon is probably the most stable solution and is extremely easy to install. That would get rid of that whole class of problems once and for all.

  • Yes, it is the correct mailbox. Normally, when e-mails are stuck in the POP connector I would load the POP mailbox into Outlook and delete them from there. It seems this time the 2 culprits were stuck in the deleted items folder on the server. I deleted them from webmail, along with some e-mails in the spam folder and the probleem seems resolved. Thanks. – Matthias Oct 24 '13 at 6:50

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