[exim] Verify problem with forwarded messages

Hello,

With two hosts XYZ1 and ABC2 both running exim, and exim.conf files containing

require verify = sender/callout


Alias MAIL1@XYZ1 is forwarded to mailbox MAIL2@ABC2.
A message from USER1@THIRD1 is sent to MAIL1@XYZ1.
USER1 is *undefined(invalid)* on domain THIRD1.

XYZ1 verifies USER1@THIRD1
since the delivering IP is defined as the SMTP server of domain THIRD1, it accepts message.
Then, it tries to deliver (forward) message to MAIL2@ABC2

Now, the delivering IP is not the SMTP server of THIRD1, instead it is the SMTP server of XYZ1.
Thus, server check fails.
Then, ABC2 tries to connect THIRD1 to check if a mail to USER1@THIRD1 can be sent.
Since USER1 is invalid on domain THIRD1, this fails too.

So, a legimate mail is rejected by ABC2 and no error message is returned to USER1@THIRD1.
In other words the message goes to :blackhole:

Either exim should replace the sender with "MAIL FROM: <>" when forwarding a message,
or it should not reject a mail when incoming machine is an SMTP server.

How can this scenario be overcome the current version of exim?
Is this a bug?

Regards.