Error: 'Cannot connect to SMTP server...' - Kerio Connect

Overview

 

Sometimes users report that their emails are not getting sent to external mail servers, domains, or recipients. The warning log shows dozens of entries similar to this:

 

[14/Jul/2019 14:50:43] Cannot connect to SMTP server <server_name>. Messages will stay in the message queue.

 

In such a situation, Message Queue in Kerio Connect Webadmin is full of emails with status 4.4.1 Cannot connect to host.

 

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Requirements

 

• Access to Kerio Connect server
• Access to firewall settings

 

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Root Cause

 

A firewall is blocking communication from the Kerio Connect server to External Mailservers.

 

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Resolution

 

To resolve the connection issue:

1. Check MX records for Kerio Connect domain (using the MX Lookup Tool). The records should be pointing to the correct mail server. The first record should be starting from mail.connect_domain.com
   
   
   
   
2. Enable additional Debug logs.
   
   
   1. Open Kerio Connect Webadmin.
   2. Navigate to Logs > Debug, right-click on logs area, and click on Clear Log.
   3. Right-click on logs and click on Messages.
   4. Enable SMTP Server, SMTP client, and Queue processing.
      
      
      
      
   5. Send a test email to the (desired) outside email address.
   6. Gather Debug logs: Navigate to Logs > Debug, right-click on logs and click on Save Log.
   7. Generate Support Information file by navigating to Status > System Health > Support Information.
      
      
3. Analyze Debug logs. You will see an output with messages similar to the below:
   
   [14/Jul/2019 19:22:31][123145371508736] {qproc} SEND_REMOTE: Started delivery of queued message id=5d2be366-00000000 sender=<username@connect_domain.com>
   [14/Jul/2019 19:22:31][123145371508736] {qproc} The default MX delivery rule is applied for sender <username@connect_domain.com> and recipient <ext_user@external_domain.com>
   [14/Jul/2019 19:22:31][123145371508736] {qproc} Scheduling recipient: ext_user@external_domain.com to a batch in rule 'external_domain.com'
   [14/Jul/2019 19:22:31][123145371508736] {smtpc} Connecting to server mail.external_domain.com (<ip_address_of_external_server>:25) using local interface 0.0.0.0 ...
   [14/Jul/2019 19:23:45][123145371508736] {smtpc} Deliver mail: Cannot connect to SMTP server. User: , server: mail.external_domain.com
   [14/Jul/2019 19:23:45][123145371508736] {qproc} SEND_MX: Result for recipient ext_user@external_domain.com: delayed, Status: 4.4.1 Cannot connect to host
   
4. Try to telnet to external_domain.com.
   
   telnet external_domain.com 25
   
   The connection will be refused.
5. Check Firewall or Antivirus settings to allow traffic flowing from SMTP standard port (25) to the outside world (external servers).

 

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Confirmation

 

If everything is okay, you will see ESMTP ready output while performing Telnet.

 

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Additional Information

 

For more information about Firewall setup, refer to Securing Kerio Connect - section 'Configuring your firewall'.

If you are using Kerio Control in front of Kerio Connect, please refer to Configuring Kerio Control Firewall to allow Kerio Connect services.

 

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