This article applies to:

• Trustwave MailMarshal (SEG)

Symptoms:

Event ID: 2503
Type: Warning
Source: MMSender
Description: Network transport error

Causes:

The remote host responded to a SMTP request from the MailMarshal SMTP Sender in an unexpected manner, or the connection was terminated without warning.

The possible causes of transport errors include:

• A misconfigured device such as a firewall or intermediate router
• Port-blocking, anti-virus software
• SMTP proxy firewall
• Rarely, a problem with the TCP subsystem on the MailMarshal server

The cause of this error is generally not the MailMarshal software. MailMarshal is only reporting the error.

More Info:

When communicating with a remote host, the MailMarshal Sender expects proper SMTP responses to the commands it issues.

If the remote host closes a connection without sending any prior indication, or the network socket is terminated unexpectedly, this error is logged.

Generally the detailed information on this event (in the MailMarshal text logs) shows a Winsock error, indicative of a general network error beyond the scope of MailMarshal. This event is tagged by MailMarshal as an error of type "SMTPSendAndExpect".