https://github.com/serghey-rodin/vesta/issues/358

To add quota display in RoundCube

edit line:
v-add-mail-account (57) & v-change-mail-account-quota (48)

str="$account:$md5:$user:mail::$HOMEDIR/$user::userdb_quota_rule=*:storage=${quota}M"

This is to override quota_rule in Dovecot see: link

in
/etc/dovecot/dovecot.conf
add:

mail_plugins = $mail_plugins quota

plugin {
  quota = maildir:User quota
  # makes it possible for user to clean INBOX after quota reached
  quota_rule2 = Trash:storage=+100M
}

In file:
/etc/dovecot/conf.d/20-imap.conf
uncomment and add:
mail_plugins = $mail_plugins quota imap_quota

In file:
/etc/dovecot/conf.d/20-pop3.conf
uncomment and add:
mail_plugins = $mail_plugins quota

This is the configuration for Dovecot

Hope this helps someone 😉