Hi i have similiar problem like here:
http://www.iredmail.org/forum/topic11833-iredmail-support-vocation-respone-unknown-user.html
email send :
from : web123 at gmail.com
to : jacka at mail.com
vocation sent back
from : jacka at mail.com
to : srs0=hmc8=v7=gmail.com=web123 at mail.com
postsrsd changing return-path from web123 at gmail.com to
srs0=hmc8=v7gmail.com=web123 at mail.com
this is no problem for me but  sieve:
Vacation's messages are always addressed to the Return-Path address
it is possible some how change this ugly to header to normal?
dovecot --version
2.2.29.1 (e0b76e3)
# 2.2.29.1 (e0b76e3): /usr/local/etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.18 (29cc74d)
doveconf: Warning: service auth { client_limit=125000 } is lower than
required under max. load (150000)
# OS: Linux 3.10.0-514.16.1.el7.x86_64 x86_64 CentOS Linux release 7.3.1611
(Core)
auth_master_user_separator = *
auth_mechanisms = plain login
auth_worker_max_count = 60
default_client_limit = 125000
default_process_limit = 25000
dict {
  quotadict = mysql:/etc/dovecot/dovecot-used-quota.conf
}
disable_plaintext_auth = no
listen = *
log_path = /var/log/dovecot.log
login_trusted_networks = xxx
mail_fsync = never
mail_gid = 2000
mail_location = maildir:/%Lh/Maildir/:INDEX=/%Lh/Maildir/
mail_max_userip_connections = 128
mail_plugins = quota zlib expire
mail_uid = 2000
maildir_broken_filename_sizes = yes
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 ihave
namespace inbox {
  inbox = yes
  location 
  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }
  mailbox Junk {
    auto = subscribe
    autoexpunge = 30 days
    special_use = \Junk
  }
  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }
  mailbox Trash {
    auto = subscribe
    autoexpunge = 30 days
    special_use = \Trash
  }
  prefix 
}
passdb {
  args = /etc/dovecot/dovecot-mysql.conf
  driver = sql
}
plugin {
  acl = vfile
  acl_shared_dict = proxy::acl
  auth_socket_path = /var/run/dovecot/auth-master
  quota = dict:user::proxy::quotadict
  sieve = /home/sieve/%Ld/%Ln/dovecot.sieve
  sieve_after = /home/sieve/dovecot.sieve
  sieve_default = /home/sieve/dovecot.sieve
  sieve_dir = /home/sieve/%Ld/%Ln
  sieve_global_dir = /home/sieve
  sieve_global_path = /home/sieve/dovecot.sieve
  sieve_max_redirects = 25
  zlib_save = gz
  zlib_save_level = 9
}
protocols = pop3 imap sieve lmtp
service auth {
  service_count = 0
  unix_listener auth-master {
    group = vmail
    mode = 0666
    user = vmail
  }
  unix_listener auth-userdb {
    group = vmail
    mode = 0660
    user = vmail
  }
}
service dict {
  unix_listener dict {
    group = vmail
    mode = 0777
    user = vmail
  }
}
service imap-login {
  process_min_avail = 16
  service_count = 0
  vsz_limit = 64 M
}
service imap {
  process_limit = 4096
}
service lmtp {
  executable = lmtp -L
  inet_listener lmtp {
    port = 24
  }
  user = vmail
}
service pop3-login {
  process_min_avail = 16
  service_count = 0
}
service quota-warning {
  executable = script /usr/local/bin/dovecot-quota-warning.sh
  unix_listener quota-warning {
    group = root
    mode = 0666
    user = root
  }
  user = root
}
ssl_ca = </etc/ssl/ca-bundle.crt
ssl_cert = </etc/ssl/xxx.crt
ssl_key =  # hidden, use -P to show it
submission_host = xxx
userdb {
  args = /etc/dovecot/dovecot-mysql.conf
  driver = sql
}
protocol imap {
  imap_client_workarounds = tb-extra-mailbox-sep
  mail_plugins = quota imap_quota mail_log notify zlib
}
protocol pop3 {
  mail_plugins = quota zlib expire
  pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
  pop3_uidl_format = %08Xu%08Xv
}
protocol lmtp {
  info_log_path = /var/log/dovecot-lmtp.log
  mail_fsync = optimized
  mail_plugins = quota sieve zlib
  postmaster_address = xxx
}
remote xxx {
  mail_max_userip_connections = 51200
}