SUMMARY

Explains the various reasons why MailEnable would be unable to send to remote servers, and the possible solutions.

DETAIL

When sending mail to a remote mail server the message is placed in the SMTP outbound message queue for delivery. The status of this queue can be determined using the administration program (under MailEnable Management->Servers->localhost->Services and Connectors->SMTP->Queues->Outbound). Reasons why email is not being sent can be determined by viewing the SMTP Debug and Activity logs and within any bounce message that is returned to the sender address.

CAUSE

Below are some reasons that can cause problems when sending to remote servers.

1. The SMTP DNS Server has not been correctly defined or is experiencing problems resolving.

2. A firewall is blocking port 25 outbound or your ISP has banned outbound SMTP traffic.

3. Your IP address is listed in a spam database and you are blacklisted.

4. No PTR record (Reverse DNS record) defined for the outbound IP address.

RESOLUTION

1. Ensure that the DNS server is working correctly and is able to resolve external domains using the Windows "nslookup" utility. Run the MailEnable Diagnostic Report. See: Article: Article ME020043 and check for DNS resolution failures. The following articles can also help troubleshoot:

Diagnostic Report reports the error: 'Could not resolve your Local Domain Name in DNS': Article ME020183

Could not resolve MX list for domain appears in my debug log: Article ME020337

2. It is possible to verify if your ISP is blocking port 25 by attempting to telnet to port 25 of a remote mail host using a command prompt on the mail server. The command is:

telnet mail.mailenable.com 25

If no response is received, try using port 587 instead of 25. If port 587 works but 25 does not, then this would indicate your service provider is blocking outbound traffic on port 25. If both fail, then it may be your own network preventing the connection.

It can sometimes be useful to telnet utility to connect to your service providers mail server if they provide this.

3. Please review the following article: Article ME020166

4. There are various DNS lookup tools that can be used to check a domains PTR record and if one exists. MailEnable provides a lookup tool that can be located here: https://www.mailenable.com/tools

Please see the following articles on how to obtain a PTR record:

Article ME020206

Article ME020115

MORE INFORMATION

Why are messages to external domains not being sent? Article ME020133

SMTP Connector Inbound Response Codes: Article ME020032

How to manually test if MailEnable can send mail to remote servers: Article ME020207

Using nslookup to check domain resolution: Article ME020292

What is a DNS PTR record?: Article ME020206

How to diagnose outgoing mail problems: Article ME020148