dovecot - May 2019 - Is it possible to (re)direct only 1 imap user to the new server

I haven't used dovecot proxy or director. If I have a setup where all my 
users 
 are connecting to HOSTNAMEOLD, is it possible to have 1 imap user that 
is
 connecting to HOSTNAMEOLD directed/forwarded to HOSTNAMENEW?
Without changing my dns settings and preferably without creating any new 
servers.
I think I can route one users mail to HOSTNAMENEW with sendmail ldap 
routing.
So the only thing I need to be able to do is have the incoming imap 
requests on 
HOSTNAMEOLD been handled by HOSTNAMENEW.


                                          
                                          
    HOSTNAMEOLD          HOSTNAMENEW      
                                          
  +--------------+     +--------------+   
  |   SENDMAIL   |     |   SENDMAIL   |   
  |      |       |     |      |       |   
  |      |       |     |      V       |   
  |      V       |     |--------------|   
  |--------------|     |    lmtp      |   
  |  NS /INBOX   |     |      |       |   
  |    mbox on   |     |      V       |   
  | block device |     |--------------|   
  |              |     |  NS /INBOX   |   
  |--------------|     |   mdbox on   |   
  |  NS /ARCHIVE |     | block device |   
  |    mdbox on  |     |              |   
  | clustered fs |     |--------------|   
  |              |     |  NS /ARCHIVE |   
  +--------------+     |    mdbox on  |   
                       | clustered fs |   
                       |              |   
                       +--------------+