install package from debian backports pool

I use the following line for backports:

deb squeeze-backports main contrib non-free

After you added the backports to sources.list make sure to run:

apt-get update

Then in order to install a package from backports you run:

apt-get -t squeeze-backports install examplename

The option -t squeeze-backports tells apt to specifically use backports for that package. It then will also pull any dependencies that are present in backports from backports. Not using the -t option could work, in case the package name does not exist in squeeze (for example linux-image-3.2.0-0.bpo.2-amd64) AND the install does not depend on packages that also have to be pulled from backports.

Also remember that as far as I know backports packages do not automatically update through a regular update (such as apt-get upgrade). You would have to run the above command again for each package in order to pull in a possible newer backported version.

Try to do a search at first:

apt-cache -t squeeze-backports search a_fancy_package

and then choose the exact name of a package from the list

apt-get install -t squeeze-backports the_fancy_package

I'd do it like this:

apt-cache -t squeeze-backports search dove | grep -v ice

and then probably

apt-get install -t squeeze-backports dovecot-core dovecot-imapd dovecot-pop3d

and whatever else you need.