bbdb.gmailfilter installs a command-line python script and an emacs command for exporting a GMail filters Atom feed from the gnus-public and gnus-private fields in BBDB.
The package can be installed using the standard python package installation procedure. Extract the tarball, then run the following command inside the extracted directory:
$ python setup.py install
This will install the command-line utility and the rpatterson-gmail.el emacs library. Then add the following to your ~/.emacs:
Once installed, the filters can be exported to a file simply by calling M-x bbdb-export-gmail-filters. You will be prompted for a file to export the filters to.
For every BBDB record that has a value in the gnus-private field, a filter will be included that matches the "To" GMail filter field on any BBDB net addresses for that record and applies the label specified in the gnus-private field value. The same is done for BBDB records with values in the gnus-public BBDB field but filters on the "From" GMail filter field instead.