Thanks for your help, we solved the problem. Your post http://www.iredmail.org/forum/post14006.html#p14006 point us the right direction.
The problem was that mapping for the catch-all address was done by the postfix at port 25. At this time the envelope address is rewritten to the catch-all address. When the email comes to the postfix at port 10025 the envelope address is already the catchall address.
Therefore we need the first postfix at port 25 to not rewrite to the catchall address. With your hints and this idea in mind we do the following four adjustments:
1) Make sure you have below settings in Postfix main.cf:
enable_original_recipient = yes
dovecot_destination_recipient_limit = 1
2) Add flag 'O' (Letter o in upper case, not digit number zero) in Postfix master.cf for transport pipe:
dovecot unix - n n - - pipe
flags=DRhuO user=[...OMIT OTHER SETTINGS HERE...]
3) In the Postfix master.cf we add the line (-o receive_override_options=no_address_mappings) after
smtp inet n - - - - smtpd
4) In the Postfix master.cf we comment out one setting (#,no_address_mappings)
127.0.0.1:10025 inet n - - - - smtpd
[...OMIT OTHER SETTINGS HERE...]
Now everything works fine. Thanks for you great work.