==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- 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 BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.9.8
- Linux/BSD distribution name and version: CentOS 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MariaDB
- 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.
====
I'm receiving rejections from several valid sites such as below:

Aug  7 00:29:27 michael1 postfix/postscreen[11759]: CONNECT from [216.161.41.2]:61908 to [192.168.99.201]:25
Aug  7 00:29:27 michael1 postfix/postscreen[11759]: PASS OLD [216.161.41.2]:61908
Aug  7 00:29:27 michael1 postfix/smtpd[12870]: connect from outlook.atkinsoncpa.com[216.161.41.2]
Aug  7 00:29:27 michael1 postfix/smtpd[12870]: Anonymous TLS connection established from outlook.atkinsoncpa.com[216.161.41.2]: TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)
Aug  7 00:29:27 michael1 postfix/smtpd[12870]: NOQUEUE: reject: RCPT from outlook.atkinsoncpa.com[216.161.41.2]: 450 4.7.1 <ATCOEXCH.atkinsoncpa.msft>: Helo command rejected: Host not found; from=<xxxx@atkinsoncpa.com> to=<xxxx@aipb.org> proto=ESMTP helo=<ATCOEXCH.atkinsoncpa.msft>
Aug  7 00:29:28 michael1 postfix/smtpd[12870]: disconnect from outlook.atkinsoncpa.com[216.161.41.2]

This is one of several that I know are valid senders.  (I've X'd out the actual user names)

I've turned off the helo checking for the moment.

Any ideas??

Thanks - Jack