nano conf.d/10-auth.conf

auth_master_user_separator = *
!include auth-master.conf.ext

doveadm pw -s SHA512-CRYPT
nano /etc/dovecot/master-users

master@domain.tld:{SHA512-CRYPT}XXXXXXXX

nano conf.d/auth-master.conf.ext

auth-master.conf.ext

# Authentication for master users. Included from 10-auth.conf.
 
# By adding master=yes setting inside a passdb you make the passdb a list
# of "master users", who can log in as anyone else.
# <doc/wiki/Authentication.MasterUsers.txt>
 
# Example master user passdb using passwd-file. You can use any passdb though.
passdb {
  driver = passwd-file
  master = yes
  args = /etc/dovecot/master-users
 
  # Unless you're using PAM, you probably still want the destination user to
  # be looked up from passdb that it really exists. pass=yes does that.
  pass = yes
}

service dovecot reload