==== 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?
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
======== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.5-1
- Linux/BSD distribution name and version: CentOS Linux release 7.2.1511 (Core)
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? Yes
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
Hello,

Any user of our mail server mail.jaika.com is not able to send mails to only one particular domain "rediffmail.com".

Mail gets bounced with following message

Reporting-MTA: dns; mail.jaika.com
X-Postfix-Queue-ID: 42E4E407FC03
X-Postfix-Sender: rfc822; hemant@jaika.com
Arrival-Date: Tue, 12 Dec 2017 17:50:31 +0530 (IST)
Final-Recipient: rfc822; ajay_mhasal@rediffmail.com
Original-Recipient: rfc822;ajay_mhasal@rediffmail.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; mx.rediffmail.rediff.akadns.net
Diagnostic-Code: smtp; 553 sorry, invalid HELO hostname (#5.7.1)

However hostname is configured in following files and DNS records forward/reverse are also correct, Output of the same is as follows

[root@mail ~]# hostname
mail.jaika.com

[root@mail ~]# grep jaika /etc/postfix/main.cf
myhostname = mail.jaika.com
myorigin = mail.jaika.com
mydomain = jaika.com
#mydomain = mail.jaika.com

[root@mail ~]# grep jaika /etc/amavisd/amavisd.conf
#$mydomain = "mail.jaika.com";  # = 'example.com';   # a convenient default for other settings
$mydomain = 'jaika.com';        # = 'example.com';   # a convenient default for other settings
#$myhostname = "mail.jaika.com";
$myhostname = 'mail.jaika.com';
dkim_key("jaika.com", "dkim", "/var/lib/dkim/jaika.com.pem");
#dkim_key("host1.jaika.com", "dkim", "/var/lib/dkim/jaika.com.pem");
#dkim_key("host3.jaika.com", "dkim", "/var/lib/dkim/jaika.com.pem");
    # For domain: jaika.com.
    #'postmaster@jaika.com'    => { d => "jaika.com", a => 'rsa-sha256', ttl =>  7*24*3600 },
    #"spam-reporter@jaika.com"    => { d => "jaika.com", a => 'rsa-sha256', ttl =>  7*24*3600 },
    "jaika.com"  => { d => "jaika.com", a => 'rsa-sha256', ttl => 10*24*3600 },
    #"host1.jaika.com"  => { d => "host1.jaika.com", a => 'rsa-sha256', ttl => 10*24*3600 },
    #"host2.jaika.com"  => { d => "host2.jaika.com", a => 'rsa-sha256', ttl => 10*24*3600 },
    # ---- End domain: jaika.com ----

Still our mails are getting bounced with following message

This is the mail system at host mail.jaika.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<ajay_mhasal@rediffmail.com>: host
    mx.rediffmail.rediff.akadns.net[202.137.234.30] said: 553 sorry, invalid
    HELO hostname (#5.7.1) (in reply to RCPT TO command)

Please help me to resolve this issue.