==== Required information ====
- iRedMail version (check /etc/iredmail-release):
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- Related log if you're reporting an issue:
====

iRedMAil 0.9.5-1
CentOS 7
MySQL (María DB)
Apache
No Pro.

Problem
=======

I'm trying to relay in a remote iRedMail Server

mydomain.com         -->             mycorpserver.com

Trying to do this:
===============

[ Server A ]   -----Relay----->  [ Server B]  ( domain names are different)

[ Server B ]  is working Okay and attending four different domains, one of those domains has the domain name of the client [ Server A ] (mydomain.com)

What is failing?
=============

Mails to XXXX@mydomain.com  are being relayed Okay by [ Server B ]

Mails to accounts like GMail, GMX, etc, are failing with following message

said: 454 4.7.1 <hide@gmail.com>: Relay access denied (in reply to RCPT TO command))

Postifx Config for the [ Server A ]
==========================

[root@appl2 postfix]# postconf -n
alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
debug_peer_level = 5
debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd $daemon_directory/$process_name $process_id & sleep 5
html_directory = no
inet_interfaces = all
inet_protocols = all
mail_owner = postfix
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
mydomain = mydomain.com
myhostname = appl2.mydomain.com
mynetworks = 127.0.0.1/8, 107.150.37.XX,[::1]/128     (XX hide)
newaliases_path = /usr/bin/newaliases.postfix
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.10.1/README_FILES
relayhost = mail.back-enterprise.com:587
sample_directory = /usr/share/doc/postfix-2.10.1/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt
smtp_tls_mandatory_ciphers = high
smtp_tls_mandatory_protocols = TLSv1
smtp_tls_secure_cert_match = nexthop
smtp_tls_security_level = secure
smtp_use_tls = yes
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination
smtpd_tls_ask_ccert = yes
unknown_local_recipient_reject_code = 550

What I missed in the configuration? or What I do need to configure it correctly.

Thanks a lot.

-Vanwatkins.