Setting iRedmail with different IP addresses for Postfix and SoGo

==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.4.2
- Deployed with iRedMail Easy or the downloadable installer? Downloadable installer
- Linux/BSD distribution name and version: Ubuntu Server 20.04
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL (MariaDB)
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Hello everyone!

We are looking to migrate over iRedmail from an existing mail server setup with Roundube mail, Postfix and dovecot. However, this setup is working on two environments i.e.
1. Postfix and Dovecot setup on one server with IP address: 192.168.1.140 (IP address mentioned is just for explaining purposes)
2. Roundcube and Apache setup on another server with IP address: 192.168.1.141

Now for reasons I can't explain, I have to use the same IP address configuration for the new iRedmail setup.

With that said, we have a test environment server with two network adapters ergo both IP addresses are allotted to one single server.

I was able to install iRedmail without any hiccups and I installed only SoGo (no Roundcube) for my webmail and it (SoGo webmail, Admin panel, netstat) is running as expected.

Firstly, I followed this tutorial https://docs.iredmail.org/send.out.emai … esses.html to setup smtp_bind_address
But with the above changes, I was not able to send/receive any emails!

Next, I reconfigured postfix with command

sudo dpkg-reconfigure postfix

after which the mynetworks section of the postfix's main.cf config file has the IP address: 192.168.1.140
So, the mynetwork section of /etc/postfix/main.cf file is saved something like this,

Making these changes and reloading postfix made it work halfway through wherein incoming emails are being received i.e. email sent to my iRedmail server is being received to my inbox.

However, I am unable to send any emails. The mails are being queued (checked via mailq command) but not actually being sent.

So, requesting your support to understand what am I doing wrong. I am also concerned whether if this is the right way to set up an alternate IP address for postfix.

Apologies beforehand for not providing any log because as I am new to this I didn't know which log file to attach for troubleshooting. Please let me know and I will attach the log(s) accordingly.

P.S. We will be primarily using SoGo for Webmail, and ActivSync on Mail clients instead of IMAP & SMTP. Email sending/receiving is being tested with external email like Gmail.