Why are messages to external domains not being sent?

SUMMARY

How to interpret errors reported in the SMTP Debug Log File when sending to a remote server/domain. MailEnable SMTP Debug and Activity Logs can be accessed through the administration program under the MailEnable Management->Servers->localhost->Services and Connectors->SMTP->logs branch.

DETAIL

When mail is sent by MailEnable to remote SMTP Servers, there are two major steps that the server takes. Firstly, it determines who to send to (via a DNS Lookup) and secondly it attempts to connect to the server and send the data.

Note: A tool for analysing these files can be downloaded from HERE. This tool allows you to correlate errors in your debug log with SMTP Transactions recorded in your Activity logs.

Log Entry	Explanation
Domain [ Domain Name ] has MX list [ Mail server 1 , Mail server 1 ]	This indicates that outbound mail is being resolved to MX records and therefore that the DNS server appears to be functioning correctly.
DNS Server could not resolve domain name ( Domain Name ) as it does not appear to be registered.	If this entry appears in the log file then the DNS Server did not return MX records for the requested domain.
DNS Server could not resolve domain name ( Domain Name ) in a timely fashion. Check DNS Server settings.	If this entry appears in the log file then the DNS Server could not be contacted. This usually means that an invalid DNS server has been specified, or the DNS Server could not be reached or it is offline.
DNS Server could not resolve domain name ( Domain Name ) as it is invalid name.	If this entry appears in the log file then the DNS Server did not return any records for the specified domain. This indicates that the domain name is misspelt or there is a problem with the DNS Server.
Communications Error: Socket connection	A firewall may be blocking access to the remote server or the remote host is offline.
Communications Error: Could not populate sockets address pack.	Either your Network Adapter DNS Settings are invalid or there is a DNS configuration with the remote server's MX record where the MX record could not be equated to an IP Address (A Record).
Mail server for domain name could not be resolved. We will keep trying and notify you if we are unable to deliver the message.	If you see an error as follows, then the remote server refused your connection request, you are on a blacklist or the remote host was offline. To check if you are on a blacklist, please see a website such as www.mxtoolbox.com.

MORE INFORMATION

Which DNS Server should be used with MailEnable?: Article ME020043

Windows DNS Server Response Codes: Article ME020055

How to troubleshoot SMTP Connectivity issues and Analyse Log Files: Article ME020170

Product:	MailEnable (All Versions)
Article:	ME020133
Module:	SMTP
Keywords:	external,SMTP,remote,debug,activity,logging,logs
Class:	INF: Product Information
Created:	12/06/2003 1:07:00 AM
Revised:	Tuesday, November 12, 2019
Author:	MailEnable
Publisher:	MailEnable