Can u please explain on this

I am using Iredmail pro on centos

In postfix configuration file there is a line for smtpd_sender restriction ,and in that enforced sender login mismatch and sender authentication
In iredmail forwarding  between  internal and external email accounts works fine, if we set forwarder on an local iredmail email account.Can u please clear my doubt on this

Suppose if i am sending  a mail using iredmail from A@example.com to B@example.com,having C@example.com set as frorwarder. mail forwarding works fine.Here is my doubt
A will deliver email to B account ,this part Ok ,but how could A deliver the same mail to C as this again needed authentication
I expected a Sender A  not Logged in Error while autoforwarding mails on same domain.like this
(reason: 553 5.7.1 <A@example.com>: Sender address rejected: not logged in)

But ired works fine

How this works in iredmail