Object with that ID already exists

Problem

LMTP rejecting messages with the exception "object with that id already exists".

Description

This issue rarely occurs when checkpoint (MySQL DB) value not updating. When this issue occurred, /opt/zimbra/log/mailbox.log will be logged with similar lines.

[LmtpServer-xxx] [name=affected.user@example.com;mid=xxx;ip=xxx.xxx.xxx.xxx;] lmtp - rejecting message from=sender@example.com,to=affected.user@example.com
com.zimbra.cs.mailbox.MailServiceException: object with that id already exists: 159560
ExceptionId:LmtpServer-xxx:1645554762772:c850cab6de85e27d
Code:mail.ALREADY_EXISTS Arg:(itemId, IID, "159560")
. 
. 
Caused by: java.sql.SQLIntegrityConstraintViolationException: (conn=20) Duplicate entry '2447-159560' for key 'PRIMARY'