Error: "421 4.4.0 [internal] no mail servers for this domain could be reached at this time"

Products

• Email Security.cloud

Issue/Introduction

Track and trace displays an error message "421 4.4.0 [internal] no mail servers for this domain could be reached at this time" as well as IP 0.0.0.0 in the view logs section.

 

Delivered Status: Retrying delivery error 421 4.4.0 [internal] no mail servers for this domain could be reached at this time

 

 

 

 

Environment

Symantec Email Security.cloud Service

Cause

The Track and Trace logs show an error stating "421 4.4.0 [internal] no mail servers for this domain could be reached at this time" and IP address as "0.0.0.0" . The combination of these 2 items indicate that the Symantec MTA could not successfully connect to the remote host.

As there was no response received from the recipient's MTA, our infrastructure inserts an internal error message.  As the response from the recipient MTA was the equivalent of an IP of nulI, the IP of 0.0.0.0 is added and displayed in the logs. This behavior is by design to report an unsuccessful connection state to the remote host.

Resolution

Possible factors that may cause this issue

1. Connection refused by remote MTA
2. Connection times out while trying to connect to the remote MTA due to a network security device such as an IPS, Traffic Shaper device or Firewall (packet inspection).
3. Firewall rule blocking connection from local MTA IP address.
4. A device on the internal network causing the connection failure on the network path.
5. Scheduled mail server power down or power outage.

Please review and allow our Symantec Email Security.cloud services IP ranges on port 25 to ensure mail delivery to your infrastructure.

Note that the "MXs" part in error message "421 4.4.0 [internal] no mail servers for this domain could be reached at this time" does not refer to MX records in context but rather stands for "Mail Exchanger".

Symantec employs an exponential retry schedule based on a retry interval of 400 seconds until the interval exceeds the Max_Retry_Interval config setting (which is currently 12 hours - 43200 seconds).
Delivery ----- Seconds ------ D-HH:MM:SS
Attempt
1 -----  ----- 400 -----  --- 0-00:06:40
2 -----  ----- 800 -----  --- 0-00:13:20
3 -----  ----- 1600 ---  ---- 0-00:26:40
4 -----  ----- 3200 ---  ---- 0-00:53:20
5 -----  ----- 6400 ---  ---- 0-01:46:40
6 -----  ----- 12800 -  ----- 0-03:33:20
7 -----  ----- 25600 -  ----- 0-07:06:40
8 -----  ----- 51200 -  ----- 0-14:13:20
After the 8th try, it will attempt to deliver the message every 12 hours, until the email is delivered or expired.  Messages expire once 7 days of delivery attempts have elapsed.