(none):/etc/postfix# dpkg -l grep -i postfix
No packages found matching -i.
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-files/Unpacked/Failed-config/Half-installed
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name                          Version                       Description
+++-=============================-=============================-==========================================================================
ii  grep                          2.5.1.ds2-4                   GNU grep, egrep and fgrep
rc  postfix                       2.2.4-1.0.1                   A high-performance mail transport agent
(none):/etc/postfix#