Hi, I use sis to deduplicate attachments, here is my `doveconf -n`
------------
auth_cache_size = 10 M
auth_failure_delay = 5 secs
auth_mechanisms = plain login
auth_socket_path = /var/run/dovecot/auth-userdb
auth_ssl_username_from_cert = yes
auth_username_format = %Ln
default_vsz_limit = 512 M
lmtp_rcpt_check_quota = yes
mail_attachment_detection_options = add-flags-on-save
mail_attachment_dir = /var/mail/mail_attachment/
mail_debug = yes
mail_gid = vmail
mail_location = maildir:/var/mail/%n/Maildir
mail_plugins = quota fts fts_solr
mail_privileged_group = vmail
mail_uid = vmail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    auto = subscribe
    special_use = \Junk
  }
  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }
  mailbox Trash {
    auto = subscribe
    special_use = \Trash
  }
  prefix =
}
passdb {
  args = /etc/dovecot/dovecot-ldap.conf.ext
  driver = ldap
}
plugin {
  fts = solr
  fts_autoindex = yes
  fts_autoindex_exclude = \Junk
  fts_autoindex_exclude2 = \Trash
  fts_solr = break-imap-search url=http://localhost:8983/solr/dovecot/
  quota = maildir:User quota
  quota_grace = 10%%
  quota_max_mail_size = 5M
  quota_over_flag_lazy_check = yes
  quota_over_flag_value = TRUE
  quota_rule = *:storage=100M
  quota_warning = storage=65%% quota-warning 65 %u
  quota_warning2 = storage=60%% quota-warning 60 %u
  sieve = file:~/sieve;active=~/.dovecot.sieve
}
protocols = imap lmtp sieve
service auth-worker {
  user = $default_internal_user
}
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0640
    user = postfix
  }
  unix_listener auth-userdb {
    mode = 0777
    user = $default_internal_user
  }
  user = $default_internal_user
}
service imap-login {
  inet_listener imap {
    port = 0
  }
  inet_listener imaps {
    port = 993
    ssl = yes
  }
}
service managesieve-login {
  inet_listener sieve {
    port = 4190
  }
  process_min_avail = 0
  service_count = 1
  vsz_limit = 128 M
}
service pop3-login {
  inet_listener pop3 {
    port = 0
  }
  inet_listener pop3s {
    port = 0
  }
}
service quota-warning {
  executable = script /usr/local/bin/quota-warning.sh
  unix_listener quota-warning {
    user = vmail
  }
  user = vmail
}
service stats {
  unix_listener stats-writer {
    mode = 0666
  }
}
service submission-login {
  inet_listener submission {
    port = 0
  }
}
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 = /etc/dovecot/dovecot-ldap.conf.ext
  default_fields = home=/var/mail/%u
  driver = ldap
}
protocol !indexer-worker {
  mail_vsize_bg_after_count = 0
}
protocol lda {
  mail_plugins = quota fts fts_solr sieve
}
protocol imap {
  mail_max_userip_connections = 5
  mail_plugins = quota fts fts_solr imap_quota
}
protocol lmtp {
  mail_plugins = quota fts fts_solr
}
---------
I try to send an email and then forward this email to another recipient. No attachment is generated in `mail_attachment_dir`.

Anything wrong ?