Roughly he told me that (sorry Daniel if this is not 100% accurate):
-apparently thunderbird does not provide a nice way of opening a
specific email via the command line
-the database format (msf files) is hard to parse
So I went to the Thunderbird forums and asked about that:
http://forums.mozillazine.org/viewtopic.php?p=1891642
And mscott, the main Thunderbird developer answer was: "Copernico and
GDS integrated with thunderbird using our APIs, no mork parsing
required. Seems like beagle should be able to do the same thing."