Overview

When an user with a Kerio Connect mailbox sends an email to an external email address using Microsoft Outlook, the message is being rejected by Kerio Connect because the user cannot relay through this server. The user is configured for SMTP Authentication in Outlook. The user has no other issues sending messages to other users on Kerio Connect domain. The error seen in the logs is:

Status: 5.5.4 Cannot find hostname "external_domain.com" in DNS, Remote-Host: external_domain.com

Solution

Access to Kerio Connect Administration is required to understand the below points.

Kerio Connect has a retry interval for SMTP messages. It can be setup in Configuration > SMTP server > Queue Options. The default value is set to 30 minutes:

The same value is configured for POP3 before SMTP (if enabled) in Configuration > SMTP server > Relay Control:

If the email delivery failed initially, Kerio Connect will retry sending the message after 30 minutes (as per the above settings). This can be confirmed in the logs:

[13/May/2020 07:06:32] Sent: Queue-ID: 9aaaaa9a9-99999add, Recipient: <user1@external_domain.com>,
Result: delayed, Status: 5.5.4 Cannot find hostname "external_domain.com" in DNS,
Remote-Host: external_domain.com, Msg-Id: <999999d62916$999999a0$4c9999e0$@domain.com>
[13/May/2020 07:36:33] Sent: Queue-ID: 9aaaaa9a9-99999add, Recipient: <user1@external_domain.com>,
Result: failed, Status: 5.1.1 550-(mail.kerio_domain.com) [vvv.xxx.yyy.zzz]:47903 is currently not permitted to
[13/May/2020 07:36:33] 550-relay through this server. Perhaps you have not logged into the pop/imap
[13/May/2020 07:36:33] 550-server in the last 30 minutes or do not have SMTP Authentication turned on
[13/May/2020 07:36:33] 550 in your email client., Remote-Host: external_domain.com,
Msg-Id: <999999d62916$999999a0$4c9999e0$@domain.com>

The initial Cannot find hostname in DNS error may occur because of external domain issues or local Outlook problems. Below are the steps to resolve this:

• Resend the email from Outlook after some time.
• If this doesn't work, then, send the email using Kerio Connect Webmail.
• If the issue persists, then reach out to the external domain user using alternative methods (chat, call, meeting, etc.).