This error message means that SmartPOP2Exchange tries to send out a message through the Exchange Server but the Exchange Server doesn't allow this.
To enable this please try the following:
The relaying permission for Exchange Server 2007/2010 and 2013 needs to be set using exchange powershell:
Get-ReceiveConnector "<you receiveconnector id/name>" | Add-ADPermission -User "NT AUTHORITY\ANONYMOUS LOGON" -ExtendedRights "Ms-Exch-SMTP-Accept-Any-Recipient"
[See Help article at Microsoft]
Restricting the receive connector to localhost only is not possible; you need to accept at least the local network too: 127.0.0.0/8 (loopback) and 192.168.0.0/16
To solve this problem you have to do a workaround using a rule. Create a global rule using the condition "Messages with a size bigger than [enter size limit here]". As action choose "Save attachments to [enter a save path here]" and check the "Add path of save attachments to message body" option. Also add the action "Forward without attachments".
Forwarding (Regarding to Exchange Server configuration please read the chapter "Setup guide for connecting Exchange Server")
Please make sure, that the SSL certificate of your server is (still) valid. As a system service, SmartPOP2Exchange is bound to assume, that your certificates are valid - so if the POP3 server delivers an invalid certificate, SmartPOP2Exchange cannot proceed without a valid certificate.
This problem does not come from SmartPOP2Exchange. It is a common problem of the 2003 Exchange Server:
If SmartPOP2Exchange changes the email header, i.e., the active Spam-Filter adds the SpamAssassin header field, then SmartPOP2Exchange will recode the header. Therefore, UTF-8 will be used when no code per content-type is indicated.
As long as SmartPOP2Exchange does not change the mail header, then the problem will not occur. That the actual problem comes from the 2003 Exchange Server.
Normally 3 mail messages are generated by the originating mail server and should finally reach the POP3/IMAP catch-all account.
But we have seen a few cases in which the receiving mail server deleted subsequent mail messages and kept only the first message in the catch-all account.
This behavior is incorrect for catch-all accounts, as these mail messages have different entries in the Envelope-To: header line.
Since version 6.1 of SmartPOP2Exchange there is an option for catch-all accounts on servers with such an incorrect behavior. This option replicates mail messages for each recipient of the TO and CC header field.
Of course this problem can also be solved by creating individual POP3/IMAP accounts for the active email addresses.