Why is 'sent' folder missing in my MUA(email client)

[luckydog xf]

hello,

    I'm successfully send and receive emails by postfix and dovecot, but
folder name 'Sent' is gone, all sent emails are located in Drafts folder.

    Anything wrong? Guess it has something to do with mailbox and location.

   Here is `doveconf -n`
------------------
auth_cache_size = 1 M
auth_debug_passwords = yes
auth_mechanisms = plain login
auth_ssl_username_from_cert = yes
auth_verbose = yes
auth_verbose_passwords = yes
import_environment = TZ
login_trusted_networks = 172.16.0.0/12
mail_location = maildir:/var/mail/%n/Maildir
mail_privileged_group = mail
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix =
}
passdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
protocols = imap lmtp
service auth-worker {
  user = $default_internal_user
}
service auth {
  unix_listener /var/spool/postfix/private/auth {
    mode = 0666
  }
}
service imap-login {
  inet_listener imap {
    port = 0
  }
  inet_listener imaps {
    port = 993
    ssl = yes
  }
}
service lmtp {
  unix_listener lmtp {
    mode = 0666
  }
}
service pop3-login {
  inet_listener pop3 {
    port = 110
  }
}
ssl = required
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
  driver = prefetch
}
userdb {
  args = uid=mail gid=mail home=/var/mail/%u
  driver = static
}
verbose_proctitle = yes

-----

  I also checked mail dir, it has /var/mail/XXX/Maildir/.send/

  So anything wrong?

Thanks,
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