Thank you for the reply.

In old server (production1), I have changed like this for passdb. rest all i kept the same.

passdb {
        args = /etc/dovecot/master-users
        driver = passwd-file
        master = yes
        #pass = yes
        }

passdb {
    driver = passwd-file
    args = username_format=%u /etc/dovecot/passwd
}

Now I am getting the below Authentication error from production2. Seems I have made some mistake.

-----
[root@production2 dovecot]# doveadm backup -a All -R -u kishore@test.testorg.com imapc:
dsync(kishore@test.testorg.com): Info: imapc(production1.testorg.com:143): Connected to 161.2.11.119:143 (local xxx.xxx.xxx.xxx:39200)
dsync(kishore@test.testorg.com): Error: imapc(production1.testorg.com:143): Authentication failed: [AUTHENTICATIONFAILED] Authentication failed.
dsync(kishore@test.testorg.com): Error: User initialization failed: imapc: Login to production1.testorg.com failed: Authentication failed: [AUTHENTICATIONFAILED] Authentication failed.
-----

In production1, I see this error:

-----
Aug 04 16:42:43 imap-login: Info: Disconnected (auth failed, 1 attempts): user=<vmail>, method=PLAIN, rip=xxx.xxx.xxx.xxx, lip=xxx.xxx.xxx.xxx
-----

The content on the password file:

-------
[root@production1 log]# cat /etc/dovecot/passwd
karan@test.testorg.com:{PLAIN}Password123
kishore@test.testorg.com:{PLAIN}Password123

[root@production1 log]# cat /etc/dovecot/master-users
karan@test.testorg.com:{PLAIN}Password123
kishore@test.testorg.com:{PLAIN}Password123
-------
I have copied the same content of the "passwd" file to "master-users" file. Actually, it should be having same content? if different, what will be the data and which format?

Please advise me, what am I making mistakes? As told you before, the dovecot versions are production1(2.0.9) and production2(2.2.36 (1f10bfa63))