If a gateway, relay, or upstream mail server IP is added to Security → Whitelist with TCP Proxy enabled, SmarterMail will treat that IP as a trusted proxy server.
If the gateway is not actually configured as a SmarterMail TCP proxy, SmarterMail will reject connections from that IP during protocol negotiation, even though the connection itself is accepted.
This typically results in log messages such as:
* NO Server is busy, try again later.
IP x.x.x.x rejected for proxy. Reason: not a configured proxy.
Observed Effects
- IMAP clients failing to connect or repeatedly retrying
- Intermittent or misleading SSL/TLS errors during connection attempts
- SMTP connections being dropped before protocol negotiation completes
- Secondary MX servers (backup gateways) deferring or queueing mail
- Mail services appearing to be listening on ports, but behaving inconsistently
Because the connection is accepted and then rejected internally, this issue can easily be mistaken for:
- a TLS certificate problem
- a firewall or port issue
- a mail client configuration error
Resolution
- Navigate to Security → Whitelist
- Locate the affected gateway or upstream server IP
- Disable TCP Proxy for that IP
- Save changes
IMAP and SMTP services should recover immediately once the setting is corrected.
