==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.6.6
- Deployed with iRedMail downloadable installer
- Linux/BSD distribution name and version: Debian 12.2.0
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin
Log:
2023-11-06T13:54:16.859187+01:00 mail postfix/smtpd[4570]: disconnect from mailout10.t-online.de[194.25.134.21] ehlo=2 starttls=1 mail=1 rcpt=0/1 data=0/1 rset=1 quit=1 commands=6/8
2023-11-06T13:54:16.908428+01:00 mail postfix/postscreen[4567]: CONNECT from [194.25.134.21]:43648 to [192.168.187.201]:25
2023-11-06T13:54:16.908649+01:00 mail postfix/postscreen[4567]: PASS OLD [194.25.134.21]:43648
2023-11-06T13:54:16.910161+01:00 mail postfix/smtpd[4570]: connect from mailout10.t-online.de[194.25.134.21]
2023-11-06T13:54:16.980645+01:00 mail postfix/smtpd[4570]: Anonymous TLS connection established from mailout10.t-online.de[194.25.134.21]: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256
2023-11-06T13:54:17.014748+01:00 mail postfix/smtpd[4570]: NOQUEUE: reject: RCPT from mailout10.t-online.de[194.25.134.21]: 550 5.1.1 <noreply@mydomain.com>: Recipient address rejected: User unknown; from=<> to=<noreply@mydomain.com> proto=ESMTP helo=<mailout10.t-online.de>

I recently installed iRedMail on my home server and I must say that everything works fine except that iRedMail (Postix) does not accept emails sent from another postfix in the same local network.

Situation:
fully functional iRedMail installed on Debian 12.2.0 virtual machine.
IP address 192.168.2.11
One domain "mydomain.com"
User 1: "pippo@mydomain.com"
One alias on user "pippo@mydomain.com": "noreply@mydomain.com"

iRedMail receives mails sent externally (from a Google account for example) addressed to both "pippo@mydomain.com" and the alias "noreply@mydomain.com"

KVM Host Server, Debian 12.2.0 on which the virtual machine is running with iRedMail and another Postfix instance is installed that sends messages and notifications from other local applications such as Wiki and NextCloud.
IP address 192.168.1.11.
The KVM Server sends eMails without problems to any external address except to any domain address "@mydomain.com"

I have tried everything, greylist, whitelist, unfortunately nothing, iRedMail keeps not accepting any eMails sent from the Postfix of the KVM Host Server.

The strange thing is that if I send a Mail from a Raspberry PI in the same network (192.168.1.12) the mail is accepted by iRedMail.

All three Postix instances use the T-Online server as a relay.

Until a few weeks ago I was using the same configuration with Kolab instead of iRedMail and everything worked perfectly, therefore I am convinced that I make some mistake in the iRedMail/Postfix configuration......

Greetings to all and thanks in advance to those who can help me.
Raggovaivo