==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.6 MARIADB edition.
- Linux/BSD distribution name and version: Centos 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): Apache
- Manage mail accounts with iRedAdmin-Pro? Yes
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Both domains: firstdomain.pl and seconddomain.pl exists in our iredmail system.
There are no users in firstdomain.pl, only aliases, forwarding emails to mail.firstdomain.pl.
smtp-proxy-1.mydomain.pl is our proxmox mail proxy .

user@firstdomain.pl tries to send an e-mail to szkolenia@seconddomain.pl and we get this in maillog:

[root@irm ~]# cat /var/log/maillog-20171112 | grep firstdomain | grep seconddomain
Nov 10 14:05:45 irm postfix/smtpd[17543]: NOQUEUE: reject: RCPT from smtp-proxy-1.mydomain.pl[111.111.14.66]: 554 5.7.1 <szkolenia@seconddomain.pl>: Recipient address rejected: Policy rejection not logged in; from=<user@firstdomain.pl> to=<szkolenia@seconddomain.pl> proto=ESMTP helo=<smtp-proxy-1.mydomain.pl>
Nov 10 14:42:06 irm postfix/smtpd[5549]: NOQUEUE: reject: RCPT from smtp-proxy-1.mydomain.pl[111.111.14.66]: 554 5.7.1 <szkolenia@seconddomain.pl>: Recipient address rejected: Policy rejection not logged in; from=<user2@firstdomain.pl> to=<szkolenia@seconddomain.pl> proto=ESMTP helo=<smtp-proxy-1.mydomain.pl>

and the sender gets :
554 5.7.1 <szkolenia@seconddomain.pl>: Recipient address rejected: Policy rejection not logged in

I suppose it's due iredapd reject_sender_login_mismatch, which i want to remain active.
How to workarount, to allow firstdomain.pl to deliver e-mails to another local domains?