Can't install with 'export DEBIAN_FRONTEND=noninteractive'

[Zhang Huangbin]

Binary package hint: postfix-policyd

Postfix-policyd can't be installed with DEBIAN_FRONTEND=noninteractive:

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# export DEBIAN_FRONTEND=noninteractive
# apt-get install postfix-policyd
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  postfix-policyd
0 upgraded, 1 newly installed, 0 to remove and 20 not upgraded.
Need to get 0B/68.8kB of archives.
After this operation, 336kB of additional disk space will be used.
Selecting previously deselected package postfix-policyd.
(Reading database ... 29247 files and directories currently installed.)
Unpacking postfix-policyd (from .../postfix-policyd_1.82-2ubuntu2_amd64.deb) ...
Processing triggers for ureadahead ...
Setting up postfix-policyd (1.82-2ubuntu2) ...
dbconfig-common: writing config to /etc/dbconfig-common/postfix-policyd.conf

Creating config file /etc/dbconfig-common/postfix-policyd.conf with new version

Creating config file /etc/postfix-policyd.conf with new version
sanity check failed for dbc_dbuser.
error encountered creating user:
No database user specified.
dbconfig-common: postfix-policyd configure: aborted.
dbconfig-common: flushing administrative password
dpkg: error processing postfix-policyd (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 postfix-policyd
E: Sub-process /usr/bin/dpkg returned an error code (1)
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