Attempts to forward to external emails results in user unknown bounce

I’ve followed the instructions in CyberPanel docs and set up mail forwarding from my email at info@mydomain.com that is housed on CyberPanel and Centos 8 on DigitalOcean to forward to two external addresses:

a.b@yahoo.com and
mydomain@gmail.com

When I send an email from an external address, say xyz@gmail.com to the info@mydomain.com, both forward addresses don’t work, only info@mydomain.com receives an email but both forwards bounce.

The undelivered error message I’m getting back at xyz@gmail.com reads as follows:
“”"""
This is the mail system at host mydomain.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

a.b@yahoo.com (expanded from info@mydomain.com): user
unknown

mydomain@gmail.com (expanded from info@mydomain.com): user unknown
“”""

Is this a known issue? What could be causing it?

Any help in getting to the bottom of it is greatly appreciated.

Simeon

Hi @sleyzerzon Can you solve the problem?