1. Can you send a copy of this undeliverable email that the ISP sent back to you?
2. You may also want to turn on debug logging on the server that your email client is sending the email through (SMTP Server of Mapping?), recreate the error by sending it to one address, and then send in the debug log file.
C:\Program Files\WinGate\Logs\SMTP Server\SMTP Server.log.
3. You might also want to send in your WinGate registry:
GateKeeper --> Options menu --> Advanced --> Save Registry settings.
http://support.qbik.com/index.php?_a=tickets&_m=submit
*P.s. Common scenario's for the email server setup is available from a whitepaper.
http://downloads.qbik.com/qbiknz2/downl ... ations.pdf
Scenario 1. Page 11: WinGate Server as the main mail server on the Network.
Scenario 2. Page 25: A mail server already exists on the network.
Scenario 3. Page 43: An ISP hosts mail for the domain.
Scenario 4. Page 64: Using WinGate as a non-internet, LAN only Mail Server.
Scenario 5. Page 75: Using WinGate mail for Multi Office / single domain