Quoting Mostafa Rokooie mostafa.rokooie@gmail.com:

I want to know is there any solution to edit an existing message in mailbox via IMAP? or replace it with a new message (store a new message with same UID)?

You **can't** alter an existing UID message. You have to re-add the
message to the mailbox and use a new UID. For this, you have 2 options:

1.) FETCH the message, alter it locally, APPEND the message to the
server, and DELETE the original message. 2.) Use CATENATE to create a new message, and DELETE the original
message (this is how we strip attachments from a message). Note that
not all IMAP4rev1 servers support CATENATE.

michael