SpamSieve stores its training data in the folder:
/Users/<username>/Library/Application Support/SpamSieve/
and it stores its preferences in the file:
/Users/<username>/Library/Preferences/com.c-command.SpamSieve.plist
To transfer SpamSieve’s data to another machine, first quit both copies of SpamSieve. Then copy the folder and the preferences file to the corresponding locations on the other machine.
When copying your SpamSieve setup to a Mac that didn’t previously have SpamSieve installed, you’ll need to put the SpamSieve application file in the Applications folder and do the setup in your mail program, but you can skip the initial training process because of the files that you copied above.