Hello,  
I've setup Dovecot and Postfix mailing systems.  The protocol is imap.  Now, I've realized that there are no "sent items, drafts" boxed under Maildir for each users.  I would like to take back up Inbox, sent items, draft boxes.  For sent items box, it seems to be stored in outlook client file which is "ost".  The configuration parameters and version is as follows.  I can see that "namespace" has been configured.  How can I setup to see these folders?

Thank you for your support!

1. Dovecot version ->2.2.36
2. dovecot -n
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#2.2.36 (1f10bfa63): /etc/dovecot/dovecot.conf
# OS: Linux 3.10.0-957.5.1.el7.x86_64 x86_64 CentOS Linux release 7.6.1810 (Core)
# Hostname: mail.corp-associe.com
auth_mechanisms = plain login
auth_verbose = yes
disable_plaintext_auth = no
first_valid_uid = 1000
listen = *
log_path = /var/log/dovecot.log
mail_debug = yes
mail_location = maildir:~/Maildir
mbox_write_locks = fcntl
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }
  mailbox Junk {
    auto = subscribe
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    auto = subscribe
    special_use = \Trash
  }
  prefix =
}
passdb {
  args = scheme=CRAM-MD5 username_format=%u /etc/dovecot/users
  driver = passwd-file
}
protocols = imap
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
}
service imap-login {
  inet_listener imap {
    port = 0
  }
  inet_listener imaps {
    port = 993
    ssl = yes
  }
}
service pop3-login {
  inet_listener pop3 {
    port = 0
  }
  inet_listener pop3s {
    port = 995
    ssl = yes
  }
}
ssl_cert = </etc/letsencrypt/fullchain1.pem
ssl_key =  # hidden, use -P to show it
userdb {
  args = username_format=%u /etc/dovecot/users
  driver = passwd-file
}
userdb {
  args = uid=vmail gid=vmail home=/var/spool/virtual/%d/%n
  driver = static
}