Overview

Kerio Connect Administrators might have noticed emails that contain attachments (over 25 MB) are missing in Outlook for Mac or Apple Mail. However, older large messages are still shown in the email clients mentioned and in webmail. Since the emails are not at all synced to Outlook for Mac/Apple Mail, they are also not searchable in these email clients.

This is because starting with version 9.2.7 there is a size limit in the EWS (Exchange Web Services) parameters, which is the protocol used by Outlook for Mac/Apple Mail for syncing the Kerio Accounts. The default value can be increased by following the steps listed in this article.

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Prerequisites

• Kerio Connect 9.2.7 and above
• macOS Outlook or Apple Mail

Diagnosis

The change in default limit was implemented because of issues related to the Kerio Connect server crashing when converting large items (bigger than 25MB) for transmission over EWS (Exchange Web Services).

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Solution 

Note: The 25MB default limit for messages can be increased. However, this could lead to stability issues. Therefore, you should be aware that if increasing the limit leads to crashes, the system needs to be modified back to the default value.

1. Stop the Kerio Connect service. For more information, refer to Starting or Stopping the Kerio Connect Server.
2. Navigate to the installation folder of the Kerio Connect server. Defaults are:
   1. Windows: C:\Program Files\Kerio\MailServer
   2. macOS: /usr/local/kerio/mailserver
   3. Linux: /opt/kerio/mailserver
3. Locate mailserver.cfg and make a backup copy of it.
4. Open mailserver.cfg with a text editor. 
5. Within the file, locate the following string: <table name="EWS">
6. Below the string, locate:
   <variable name="MaxPerItemResponseSize">26214400</variable>
   
   
    
7. Increase the variable value to a number (in bytes) that is suitable for the environment.
8. Save the changes made to the file.
9. Start the Kerio Connect service. For more information, refer to Starting or Stopping the Kerio Connect Server.

Note: The message limit cannot be configured on a "per user" basis; it is a server-wide parameter.

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Confirmation

Messages are displayed in accordance with the new specified limit.

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