Unable to relay message to recipient domain .Error Please turn on SMTP Authentication in your mail client

Products

• Email Security.cloud

Issue/Introduction

Unable to relay message to recipient domain .Error Please turn on SMTP Authentication in your mail client. In Track and Trace when we run the message tracking using the failure recipient domain parameter  and check the Log view we get the below error 

Status550-Please turn on SMTP Authentication in your mail client. 550-mailx.bemtaxx.messagelabs.com [xxx.xxx.xxx.x]:15387 is not permitted to 550 relay through this server without authentication.

Log view also shows the connectivity with the recipient domain is not working and there are many delivery attempts as shown below and then connectivity is established.

Delivery attempt #12022-12-16 01:54:55 AM
Recipient server: 0.0.0.02022-12-16 01:54:55 AM

Response: 421 4.4.4 [internal] Domain Does Not Resolve2022-12-16 02:01:17 AM
Delivery attempt #22022-12-16 02:01:17 AMRecipient server: 0.0.0.02022-12-16 02:01:17 AM

Response: 421 4.4.4 [internal] Domain Does Not Resolve2022-12-16 02:16:43 AM
Delivery attempt #3 (final)2022-12-16 02:16:43 AM

Recipient server: xxx.xx.xx.xx (domain .com) 2022-12-16 02:16:43 AM

 

Please Note: domain .com here represent the recipient domain for which delivery is attempted.

 xxx.xx.xx.xx  Represent the A record of the  recipient domain for which delivery is attempted.

 

Environment

Email security cloud 

Delivery direction :Outbound

Cause

MessageLabs delivery servers attempt to deliver emails to the MX record of the recipient domain, if the MX record isn't available, then MessageLabs deliver the email to A record. Since the A record is not authorized to deliver the mail the authentication fails and hence we get the error "Status550-Please turn on SMTP Authentication in your mail client. 550-mailx.bemtaxx.messagelabs.com [xxx.xxx.xxx.x]:15387 is not permitted to 550 relay through this server without authentication"

Once the MX record is available then the Mail is delivery via MX record and issue is no experienced.

Resolution

Need to contact Recipient domain Administrator /owner and  Recipient domain DNS administrator needs to fix the  issues related to their domain and its MX record . once DNS issues are fixed the Mail delivery is attempted via MX record and issue is no longer experienced.