SMTP Code: "421 4.4.0 [internal] failed to connect: no mail servers for this domain could be reached at this time"

Products

• Messaging Gateway

Issue/Introduction

• Symantec Messaging Gateway (SMG) cannot deliver some outbound emails
• Emails stay in the delivery queue with the message "421 4.4.0 [internal] failed to connect: no mail servers for this domain could be reached at this time."

Message Audit Log shows:

Error 421 4.4.0 [internal] failed to connect: no mail servers for this domain could be reached at this time.
Attempted Delivery to: default-non-local-route

Delivery queue shows:

Route: default-non-local-route
Last error: Error 421 4.4.0 [internal] failed to connect: no mail server for this domain could be reached at this time.

Environment

• Non-local messages SMTP Delivery Bindings under Advanced SMTP configuration is configured to Auto
• The network allows SMG outbound IP addresses to connect to external MTA's using only port 25

Cause

If outbound delivery to most domains is working as expected and the issue is limited to a small number of domains / mail routes, the issue is likely with the destination mail server

• The destination mail server is unreachable or offline

If all outbound email is failing with this delivery status, the issue is likely the SMG configuration

• Outbound emails were sent with the inbound IP due to Non-local messages SMTP Delivery Bindings under Advanced SMTP configuration is configured to Auto.
• The SMG inbound IP is not allowed to reach the remote domain(Usually firewall reject the connection).

Resolution

Set the Non-local messages in the Advanced SMTP configuration to use the Outbound_IP. Check the information and set the Advanced SMTP configuration to the requirements of your organization.

See SMTP advanced settings for delivery bindings.

Applies to

• Scanner with two IP addresses; one IP address for inbound connections, and the other IP address for outbound connections.
• The Advance SMTP configuration shows: Non-local messages: Auto
• The SMG inbound IP is not allowed to reach the remote domain(Usually firewall reject the connection).
• Run the following commands in an SSH session on the Symantec Messaging Gateway appliance, which will show either a successful or unsuccessful result:
   
  • telnet -b inbound_ip remote_server_ip 25
Connection refused (Unsuccessful)
     
  • telnet -b outbound_ip remote_server_ip 25
Connected to remote_server_ip (Successful)

Additional Information

For complete details on how to test mail delivery issues, reference the section, "Outbound messages in the delivery queue are not being delivered" in the document, Troubleshoot email delivery issues using telnet