dovecot - Mar 2018 - question about quota setting with postfix and dovecot

Dear dovecot-list,

I have questions regarding setting up quota with postfix(Maildir format)+
dovect. My main point of the question is to know how the user password is
used in quota in this case. Please see the below configuration info and my
questions are in the bottom.

Here are what have been done:

<Postfix side configuration>

/etc/postfix/main.cf:

-----
myhostname = mail.example.com
mydomain = example.com
myorigin = $mydomain
inet_interfaces = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
home_mailbox = Maildir/

mailbox_command = /usr/libexec/dovecot/dovecot-lda -f "$SENDER" -a
"$RECIPIENT" -d "$USER"   <--Add
-----

<Dovecot side configuration>
1.
/etc/dovecot/conf.d/10-auth.conf:

#!include auth-system.conf.ext
#!include auth-sql.conf.ext
#!include auth-ldap.conf.ext
!include auth-passwdfile.conf.ext       <---Only enabled
#!include auth-checkpassword.conf.ext
#!include auth-vpopmail.conf.ext
#!include auth-static.conf.ext

2.
/etc/dovecot/conf.d/10-master.conf

service auth {
snip/
unix_listener auth-userdb {
mode = 0666                              <---The permission for userdb 666
#user #group snip/

3.
/etc/dovecot/conf.d/10-mail.conf:

mail_location = maildir:~/Maildir
snip/
mail_plugins = $mail_plugins quota      <---set the plugin
snip/

4.
/etc/dovecot/conf.d/15-lda.conf:

snip/
postmaster_address = root at example.com   <---Add postmaster
snip/
protocol lda {
    mail_plugins = $mail_plugins        <--set the plugin
}

5.
/etc/dovecot/conf.d/20-imap.conf:

protocol imap {
    mail_plugins = $mail_plugins imap_quota   <--set the plugin
snip/

6.
/etc/dovecot/conf.d/20-pop3.conf:

snip/
protocol pop3 {
    mail_plugins = $mail_plugins quota   <--set the plugin
snip/

7.
/etc/dovecot/conf.d/90-quota.conf:

plugin {                                <--set global quota
    quota = maildir:<User quota>
    quota_rule = *:storage=100M
    quota_rule2 = Trash:storage=+100M
}

8.
/etc/dovecot/conf.d/auth-passwdfile.conf.ext:

snip/
passdb {
    driver = passwd-file
    args = scheme=CRYPT username_format=%u /etc/dovecot/users    <--Path
for passwdfile
}

userdb {
    driver = passwd-file
    args = username_format=%u /etc/dovecot/users
}
snip/

9.
/etc/dovecot/users:

test004:{SSHA256}hFxB8tbyZrCCcwZKDaQEiUfojbRovOq8ECU0syPHQTCY0233:18222:18222::/home/test004::userdb_quota_rule=*:storage=1M
test005:{SSHA256}hFxB8tbyZrCCcwZKDaQEiUfojbRovOq8ECU0syPHQTCY0233:18223:18223::/home/test005::userdb_quota_rule=*:storage=1M
test006:{SSHA256}hFxB8tbyZrCCcwZKDaQEiUfojbRovOq8ECU0syPHQTCY0233:18224:18224::/home/test006::userdb_quota_rule=*:storage=1M

Note:The hashed password is created running the blow command:

# doveadm pw -s ssha256

10.
/etc/dovecot/dovecot.conf:

snip/
protocols = imap pop3     <--Available protocols
snip/

11.
# service postfix restart
# service dovcot restart


Question:
1./etc/dovecot/users is supposed to be seen instead of /etc/passwd for
authentification of imap and pops in receiving emails, isn't it?
2.If the answer for above question 1 is 'YES', then doesn't it
require to
get all password in /etc/passwd hashed for each user and place all of them
into /etc/dovecot/users?
3.If the answer for above question 1 is 'NO', then what the
hashed-password
in /etc/dovcot/users such as {SSHA256}hFX... used for?

Excuse me if those are silly questions, but I am not a dovecot person and
would very much appreciate it if anyone would kindly give me a hand on this.

Regards,
Masaharu Kawada
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