How to fix Result: delayed, Status: 4.3.0 Recipient's mailbox busy on Kerio Connect

When a resource is tied up and cannot be used by another part of the mailserver process, the following error is shown in the Mail logs: "Result: delayed, Status: 4.3.0 Recipient's mailbox busy."

As a result, the user mailbox can't send or receive any emails. The email account in Kerio Connect Webmail returns the initializing icon and then times out. The Outlook for Mac configured via IMAP might experience intermittent connection fails, due to which there might also be a delay in incoming mails.

1. User/s who are seeing the issue should log out of all the mail sessions, for example, Outlook, WebMail, etc.

2. Stop the Kerio Connect service (Windows, macOS/Linux).

3. Navigate to the Kerio Connect store folder.

4. Navigate to the <store>/mail/domain/user/<folder_name>/ directory.

5. Locate the index.fld file and rename it to index.bad.

   Note: The file extension must be renamed specifically to .bad.

6. Start the Kerio Connect service (Windows, macOS/Linux).

7. User/s who were seeing the issue should now login.

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