Mails sent from alias rejected by gateway.

Hello

I am using an on premise exchange server (but the same behavior is with O365).
Scenario/setup:
Exchange 2 domains: domain1.com and domain2.com and setup in Sophos Central with inbound and outbound mail flow through central email and ADSync for users/mailboxes.
2 mailboxes setup with:
Mailbox1: SMTP:primaryemail1@domain1.com, smtp:aliasemail1@domain1.com, smtp:aliasemail1@domain2.com
Mailbox2: SMTP:primaryemail2@domain2.com, smtp:aliasemail2@domain1.com, smtp:aliasemail2@domain2.com

Behavior (email sent to external recipient through Sophos central):
Sent from SMTP:primaryemail1@domain1.com – OK
Sent from smtp:aliasemail1@domain1.com – OK
Sent from smtp:aliasemail1@domain2.com – rejected by Sophos Central
Sent from SMTP:primaryemail2@domain2.com – OK
Sent from smtp:aliasemail2@domain1.com – rejected by Sophos Central
Sent from smtp:aliasemail2@domain2.com – OK

Conclusion:
If I send an email from an alias address which has a different domain then the primary address then Sophos Central is rejecting the email and not delivering it to the final recipient even both domains are set up in Sophos Central.

I have a support case (05321938) open since 06/2022 about this problem, but no solution has been found.
Has anyone run into the same problem and found a solution for it?

Thanks’ with kind regards.
Günter