[arch-general] Postfix delivery problem

[G. Schlisio]

Dear list,

We have a mail server with postfix and dovecot where we have mail
addresses with local unix accounts (authenticated by pam) and without
unix accounts (dovecot passwd-file authentication). The problem only
affects those non-unix account mail addresses. (There are also
completely virtual email addresses with different domains, also managed
by dovecot, but still working fine, for simplicity ignored here; sorry
the config is really complicated).

All non-unix-account addresses are listed in a postfix table,
configured in main.cf by:
mailbox_transport_maps = hash:/etc/postfix/mailbox_transport_maps

looking like this:
user1  dovecot
user2  dovecot

All this was working fine, before yesterdays (rather big)
system-upgrade.
Now we get the following error in the mail logs:

<user at dukun.de>: delivery via local: user lookup error

postfix/local in verbose mode complains:

postfix/local[27333]: deliver_switch[2]: local user recip user at dukun.de
exten  deliver user at dukun.de exp_from
dukun postfix/local[27333]: deliver_alias[3]: local user recip
user at dukun.de exten  deliver user at dukun.de exp_from
dukun postfix/local[27333]: deliver_alias:
hash:/etc/aliases(0,lock|no_regsub|no_proxy|no_unauth|fold_fix|utf8_request):
user not found
dukun postfix/local[27333]: dict_pcre_lookup:
/etc/postfix/aliases_regex: user
dukun postfix/local[27333]: deliver_alias:
pcre:/etc/postfix/aliases_regex(0,lock|no_regsub|no_proxy|no_unauth|fold_fix|utf8_request):
user not found
Dez 23 01:56:03 dukun postfix/local[27333]: deliver_dotforward[3]: local
user recip user at dukun.de exten  deliver user at dukun.de exp_from
postfix/local[27333]: warning: error looking up passwd info for user:
Invalid argument

It seems like postfix/local is ignoring the mailbox_transport_maps
option and trying to deliver itself instead of passing to dovecot, thus
finding no entry in the system passwd.
After full upgrade config files were merged (no changes in mail config)
and a reboot was done. The list of upgraded packages is shown at
http://termbin.com/k5ql . As downgrading postfix, dovecot and icu
(linking) did not resolve this issue, we are very confused.

As this is critical infrastructure for some people, any help is warmly
appreciated.

regards
georg