SBS POP3 connector error: invalid header fields

If you are using the POP3 Connector on Windows SBS 2008, you may encounter this error in the event log:

One or more (5) 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.

By default the POP3 connector will stop processing new messages after 5 protocol errors so once this happens, you will not receive any email.

Increase the MaxProtocolErrors from 5 to something bigger:

Set-ReceiveConnector -identity ($Env:computername + “\Windows SBS Fax Sharepoint Receive ” + $Env:computername) -MaxProtocolErrors 300

Next step: remaining messages to be downloaded, but the messages with invalid headers will still not be downloaded.
To fix this:

Set-ReceiveConnector -Identity ($Env:computername + “\Windows SBS Fax Sharepoint Receive ” + $Env:computername) -DefaultDomain $Env:UserDNSDomain

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