There is an importer utility that you can use in order to import email archives into CanIt Archiver. It's a command line utility script. If you already have the Archiver installed, you most likely already have this tool, which is called:
If not you can install it by running:
"apt-get install canit-archive-importer".
It has a man(ual) page and passing --help will display a list of options you can pass to it.
There are a few key notes that I would like to mention about this utility script here. It supports PST and MBOX format, but due to PST being a proprietary format, and having many different variations and versions, not all of them are supported. You will get the best chance of importing your archive if you can convert it into MBOX format before passing it to this script.
One other pitfall that some users encounter is that if the emails addresses in the body of archive are not the same as the one of the destination account, then CanIt cannot determine the stream, thus they will not get imported to the destination account. In this case you will need to specify the stream name manually and pass it as an argument to the script. This script is not officially supported, mostly due to its weak support for PST format, and the complexity of email archives uses already may have. Oh, and I advise to run the script in "dryrun" (--dryrun) mode prior to your actual attempt at importing to archive to make sure you have passed proper arguments to it.