Recipient address rejected: Domain not found

Hi.
I'm experiencing some issues with email delivery.
In some cases I receive an undelivered mail returned to sender that tells:
No se puede localizar a los destinatarios siguientes:
'Name' en 13/07/2023 13:39
Error del servidor: '450 4.1.2 <[email protected]>: Recipient address rejected: Domain not found'
I've checked the server resolves domainname.es properly (ping). Then I don´t know where is the problem.
Can you help me?
Thanks.

 

Does domainname.es have a valid MX record?

 

i've had one client complain about gettings this same message a few times recently for a couple of different recipient domains, sending from their mail client via their mailbox account on our ispconfig mailserver with the target recipient being a mailbox on an external mailserver.
looking through the logs on both the mailserver and dns servers (both isponfig). the mailserver queries 127.0.0.53 for the target domain, that queries our dns server (all our servers are configured to use our own dns servers 1st) which appears to immediately respond with a domain not found message.
yet a minute later, trying to send the same email to the same recipient goes through successfully without a single issue.

only had the one client complain about anything like this.. i've increased logging on bind9 on the dns servers, see if i can find any issue with recursive queries when this happens.. but no new reports of this happening to check against yet.
i'm wondering if somethings going wrong with a particular dns server somewhere over the last few days / week.

i've tried it with nslookup as well.. for the domains the clients complained about.. not even going anywhere near our own dns servers... just from my own local pc, i can get a response with **server can't find <domain.tld> : NXDOMAIN
then immediately try again and get the domains A/AAAA records returned..

 

This is not unusal for huge DNS Server Clusters like 8.8.8.8 or 1.1.1.1 the load balancing directs your query to one of the backend machines which will anwers your request. If a DNS Record is new or got changed recently the the machine that answers you might be not aware of the new entry which will result in an incorrect answer. Maybe the machine in the backend is faulty and didn't update in a long time or has other errors and results in NXDOMAIN. On the next request you get another working and up to date machine and a correct response.

 

Hi.
I don't know if domainame.es has a valid MX record. This is not my domain. this belongs to a advisory company. Not mine.
I receive an email from domainname.es in a mailbox which is configured in my ispconfig, when I tried to reply (from Outlook) I receive the error.
I don't believe domainname.es has a bad configuration. And if my server resolves the ip from that domain I don´t know about that error.
Thanks.

 

You could simply check that from the command line with dig for example:

Code:

dig MX domainname.es

Or use a website like MXToolbox for this.

When you run "host domainname.es" from you ISPConfig Server what is the result?

 

Hi.
First I run "host domainname.es" command and it shows an error.
Second. I use dig MX command, it resolves MX domainname.es.mail.protection.outlook.com
Then I believe domainname.es is hosted by Microsoft or the email belongs to O365.
Third. I run "host domainname.es" again and this way it resolves: domainname.es has address xx.xx.xx.xx
domainname.es mail is handled by 0 domainname.es.mail.protection.outlook.com

 

Looks like the mail is not handeld by domainname.es.mail.protection.outlook.com then. As till already mentioned the error "Recipient address rejected: Domain not found" indicates that the domain is not known by the receiving server.

 

We have started experiencing the same on our ispconfig server. I'd reboot the server and it will work for a few days before the email was rejected and the same "Recipient address rejected: Domain not found" message is sent to the sender.