Hi, i got this in the log:

==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):  0.9.9
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: Distributor ID:

Debian
Description:    Debian GNU/Linux 8.11 (jessie)
Release:        8.11
Codename:       jessie

- Store mail accounts in which backend (LDAP/MySQL/PGSQL):  PGSQL
- Web server (Apache or Nginx): Apache2
- Manage mail accounts with iRedAdmin-Pro? No

- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Jul  8 11:58:37 server348 postfix/submission/smtpd[21079]: connect from p2E5053E4.dip0.t-ipconnect.de[46.80.83.228]
Jul  8 11:58:37 server348 postfix/submission/smtpd[21079]: warning: connect to Milter service inet:127.0.0.1:8893: Connection refused
Jul  8 11:58:41 server348 postfix/submission/smtpd[21079]: NOQUEUE: reject: RCPT from p2E5053E4.dip0.t-ipconnect.de[46.80.83.228]: 554 5.7.1 <p2E5053E4.dip0.t-ipconnect.de[46.80.83.228]>: Client host rejected: Access denied; from=<> to=<> proto=ESMTP helo=<[192.168.1.171]>
Jul  8 11:58:41 server348 postfix/cleanup[21091]: D4CE578542: message-id=<20190708095841.D4CE578542@>
Jul  8 11:58:41 server348 postfix/qmgr[797]: D4CE578542: from=<double-bounce@cc>, size=1387, nrcpt=1 (queue active)
Jul  8 11:58:41 server348 postfix/submission/smtpd[21079]: disconnect from p2E5053E4.dip0.t-ipconnect.de[46.80.83.228]
Jul  8 11:58:41 server348 postfix/pipe[21093]: D4CE578542: to=<postmaster@>, relay=dovecot, delay=0.04, delays=0.01/0/0/0.03, dsn=2.0.0, status=sent (delivered via dovecot service)
Jul  8 11:58:41 server348 postfix/qmgr[797]: D4CE578542: removed

Postfix SMTP Error Mail:

Transcript of session follows.

Out: 220  ESMTP Postfix
In:  EHLO [192.168.1.171]
Out: 250-
Out: 250-PIPELINING
Out: 250-SIZE 15728640
Out: 250-ETRN
Out: 250-STARTTLS
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250 DSN
In:  STARTTLS
Out: 220 2.0.0 Ready to start TLS
In:  EHLO [192.168.1.171]
Out: 250-
Out: 250-PIPELINING
Out: 250-SIZE 15728640
Out: 250-ETRN
Out: 250-AUTH PLAIN LOGIN
Out: 250-AUTH=PLAIN LOGIN
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250 DSN
In:  MAIL FROM:<>
Out: 250 2.1.0 Ok
In:  RCPT TO:<>
Out: 554 5.7.1 <p2E5053E4.dip0.t-ipconnect.de[46.80.83.228]>: Client host
     rejected: Access denied
In:  DATA
Out: 554 5.5.1 Error: no valid recipients
In:  QUIT
Out: 221 2.0.0 Bye

The recipients are valid. Also the users are not banned or anything. If i send emails via those users to another its all working. but if my friend who  uses those email adresses sends them this error happens.

POSTCONF -n

sudo postconf -n
alias_database = hash:/etc/postfix/aliases
alias_maps = hash:/etc/postfix/aliases
allow_min_user = no
allow_percent_hack = no
biff = no
body_checks = pcre:/etc/postfix/body_checks.pcre
broken_sasl_auth_clients = yes
command_directory = /usr/sbin
config_directory = /etc/postfix
content_filter = smtp-amavis:[127.0.0.1]:10024
daemon_directory = /usr/lib/postfix
data_directory = /var/lib/postfix
debug_peer_level = 2
debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd $daemon_directory/$process_name $process_id & sleep 5
disable_vrfy_command = yes
dovecot_destination_recipient_limit = 1
enable_original_recipient = no
error_notice_recipient =
header_checks = pcre:/etc/postfix/header_checks
inet_interfaces = all
inet_protocols = all
lmtp_tls_mandatory_protocols = !SSLv2 !SSLv3
lmtp_tls_protocols = !SSLv2 !SSLv3
mail_owner = postfix
mailq_path = /usr/bin/mailq
message_size_limit = 15728640
milter_default_action = accept
mlmmj_destination_recipient_limit = 1
mydestination = $myhostname, localhost, localhost.localdomain
mydomain =
myhostname =
mynetworks = 127.0.0.1
myorigin =
newaliases_path = /usr/bin/newaliases
notify_classes = 2bounce, delay, resource, software, policy, data
postscreen_access_list = permit_mynetworks, cidr:/etc/postfix/postscreen_access.cidr
postscreen_blacklist_action = enforce
postscreen_dnsbl_action = enforce
postscreen_dnsbl_reply_map = texthash:/etc/postfix/postscreen_dnsbl_reply
postscreen_dnsbl_sites = zen.spamhaus.org=127.0.0.[2..11]*3
postscreen_dnsbl_threshold = 2
postscreen_dnsbl_whitelist_threshold = -2
postscreen_greet_action = enforce
proxy_read_maps = $canonical_maps $lmtp_generic_maps $local_recipient_maps $mydestination $mynetworks $recipient_bcc_maps $recipient_canonical_maps $relay_domains $relay_recipient_maps $relocated_maps $sender_bcc_maps $sender_canonical_maps $smtp_generic_maps $smtpd_sender_login_maps $transport_maps $virtual_alias_domains $virtual_alias_maps $virtual_mailbox_domains $virtual_mailbox_maps $smtpd_sender_restrictions
queue_directory = /var/spool/postfix
recipient_bcc_maps = proxy:pgsql:/etc/postfix/pgsql/recipient_bcc_maps_user.cf proxy:pgsql:/etc/postfix/pgsql/recipient_bcc_maps_domain.cf
recipient_delimiter = +
relay_domains = $mydestination proxy:pgsql:/etc/postfix/pgsql/relay_domains.cf
sender_bcc_maps = proxy:pgsql:/etc/postfix/pgsql/sender_bcc_maps_user.cf proxy:pgsql:/etc/postfix/pgsql/sender_bcc_maps_domain.cf
sendmail_path = /usr/sbin/sendmail
setgid_group = postdrop
smtp-amavis_destination_recipient_limit = 1
smtp_tls_CAfile = $smtpd_tls_CAfile
smtp_tls_loglevel = 0
smtp_tls_mandatory_protocols = !SSLv2 !SSLv3
smtp_tls_note_starttls_offer = yes
smtp_tls_protocols = !SSLv2 !SSLv3
smtp_tls_security_level = may
smtpd_data_restrictions = reject_unauth_pipelining
smtpd_end_of_data_restrictions = check_policy_service inet:127.0.0.1:7777
smtpd_helo_required = yes
smtpd_helo_restrictions = permit_mynetworks permit_sasl_authenticated check_helo_access pcre:/etc/postfix/helo_access.pcre reject_non_fqdn_helo_hostname reject_invalid_helo_hostname
smtpd_milters = inet:127.0.0.1:8893
smtpd_recipient_restrictions = reject_unknown_recipient_domain reject_non_fqdn_recipient reject_unlisted_recipient check_policy_service inet:127.0.0.1:7777 permit_mynetworks permit_sasl_authenticated reject_unauth_destination
smtpd_reject_unlisted_recipient = yes
smtpd_reject_unlisted_sender = yes
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
smtpd_sasl_path = private/dovecot-auth
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_sender_login_maps = proxy:pgsql:/etc/postfix/pgsql/sender_login_maps.cf
smtpd_sender_restrictions = reject_unknown_sender_domain reject_non_fqdn_sender reject_unlisted_sender permit_mynetworks reject_sender_login_mismatch permit_sasl_authenticated check_sender_access pcre:/etc/postfix/sender_access.pcre
smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/letsencrypt/live/mailserver/fullchain.pem
smtpd_tls_dh1024_param_file = /etc/ssl/dhparams.pem
smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CDC3-SHA, KRB5-DE5, CBC3-SHA
smtpd_tls_key_file = /etc/letsencrypt/live/mailserver/privkey.pem
smtpd_tls_loglevel = 0
smtpd_tls_mandatory_protocols = !SSLv2 !SSLv3
smtpd_tls_protocols = !SSLv2 !SSLv3
smtpd_tls_security_level = may
swap_bangpath = no
tls_random_source = dev:/dev/urandom
transport_maps = proxy:pgsql:/etc/postfix/pgsql/transport_maps_user.cf proxy:pgsql:/etc/postfix/pgsql/transport_maps_domain.cf proxy:pgsql:/etc/postfix/pgsql/transport_maps_maillist.cf
unknown_local_recipient_reject_code = 550
virtual_alias_domains =
virtual_alias_maps = proxy:pgsql:/etc/postfix/pgsql/virtual_alias_maps.cf proxy:pgsql:/etc/postfix/pgsql/domain_alias_maps.cf proxy:pgsql:/etc/postfix/pgsql/catchall_maps.cf proxy:pgsql:/etc/postfix/pgsql/domain_alias_catchall_maps.cf
virtual_gid_maps = static:2000
virtual_mailbox_base = /var/vmail
virtual_mailbox_domains = proxy:pgsql:/etc/postfix/pgsql/virtual_mailbox_domains.cf
virtual_mailbox_maps = proxy:pgsql:/etc/postfix/pgsql/virtual_mailbox_maps.cf
virtual_minimum_uid = 2000
virtual_transport = dovecot
virtual_uid_maps = static:2000
postconf: warning: /etc/postfix/main.cf: unused parameter: mtpd_banner="Your personal Mail Server"
postconf: warning: /etc/postfix/main.cf: unused parameter: non-smtpd_milters=$smtpd_milters