Connect. Communicate. Collaborate. Securely.

Home » Kerio User Forums » Kerio Connect » Mailserver 6.2 SMTP Problem

Messages: 3
Karma: 0
Send a private message to this user
Hello together !

I have to configure a mailserver in our office in Germany and Kerio Mailserver is totally new for me.

First of all some facts:

- mailserver is installed on same machine i work with (for testing)
- internal domain in our office (homezone.local)
- DSL connection with dynamic IP
- pop3-account at german ISP "1und1" for testing

I managed to configure the POP3 account, so the mailserver is able to receive emails from my ISP's pop3 server "" and forward them to my internal e-mail address "admin<_at_>homezone.local". That works fine and i can look at my mails via the Kerio Webmail-Client or Outlook.

The problem is when i try to send mails from my domain-internal Mail-Address to my external Address at 1und1. I configured Kerio Mailserver (Configuration -> SMTP Server -> SMTP Delivery), so it should be able to send mails over smtp ?! The log file reports the following:

[04/Aug/2006 10:42:54] Recv: Queue-ID: 44d3088e-00000003, Service: SMTP, From: <admin<_at_>homezone.local>, To: <xyz<_at_>>, Size: 1335, Sender-Host:
[04/Aug/2006 10:43:27] Sent: Queue-ID: 44d3088e-00000003, Recipient: <xyz<_at_>>, Result: delayed, Status: 4.1.8 421 dns lookup failed for sender domain

I have no experiences with more complex mailservers so far, but i think it's a more generell problem with DNS and so on.

I would be very thankful, if someone could help me :)


Messages: 20
Karma: 0
Send a private message to this user
Hi from Germany to Germany :-)
You?re right it?s a (kind of) DNS Problem.

The 1und1 mailserver try to resolve your Domain Name (, after this resolve it will do an reverse lookup at your IP.
The mailserver compares your Domain with your IP and vice verca.
If there?s a difference you will get this error message.

Even if you don?t send your mails via relay host, you have to look that your IP will be resolved in www, and that a reverse lookup with your IP will get the same Domain.
Concerning Spam a lot of mailserver will bounce emails that won?t pass this test above.

Hope I could help you

Messages: 80
Karma: 0
Send a private message to this user
It's an security feature from 1und1.

Call support from 1und1 and tell them that you are trying to config the SMTP to be relayed by 1und1.

Also tell them that you have your own mailserver and that you are not using exchange.

Please be aware if you have a catch all account it must be configured that it is not possible to send mails with this adress. Otherwise they deny the SMTP Relay.

We have our server also relayed with the SMPT from 1und1.

Dynamic IP is not a problem.

Messages: 14
Karma: 0
Send a private message to this user

another option would be the use of one of these dynamic dns services like dyndns.
Set up your primary domainname to this dyndns service name ( and create one or more internal domainnames.
Now, 1und1 mailserver will be able to make these reverse dns lookups to your dyndns adress.

Previous Topic: Can Outlook publish Free/Busy WITHOUT the connector?
Next Topic: Accessing Contacts from 4D
Goto Forum:

Kerio discussion forums are intended for open communication between forum members and may contain information and material posted by members which may be useful in learning about Kerio products. The discussion forums are not intended to provide technical support for any specific product. Any information implied or expressed in the discussion forums is that of the posting member. Kerio is in no way responsible for the information posted in the forums, or its accuracy. Kerio employees may participate in the discussions, but their postings do not represent an offical position of the company on any issues raised or discussed. Kerio reserves the right to monitor and maintain the forums to promote free and accurate exchange of information.

Current Time: Tue Nov 21 16:54:09 CET 2017

Total time taken to generate the page: 0.00352 seconds
.:: Contact :: Home ::.
Powered by: FUDforum 3.0.4.