Does spamassassin simply total up the scores of all the tests which are found to be valid for a message, or does it increase the score based on whether a combination of tests exist?
Sometimes. SpamAssassin has both additive rules (each hit is worth a set number of points) and "meta" rules (where certain combinations of hits are worth more than the sum of the individual rules hit).
smime.p7s
Description: S/MIME Cryptographic Signature
This message is intended only for the use of the person(s) listed above as the intended recipient(s), and may contain information that is PRIVILEGED and CONFIDENTIAL. If you are not an intended recipient, you may not read, copy, or distribute this message or any attachment. If you received this communication in error, please notify us immediately by e-mail and then delete all copies of this message and any attachments.
In addition you should be aware that ordinary (unencrypted) e-mail sent through the Internet is not secure. Do not send confidential or sensitive information, such as social security numbers, account numbers, personal identification numbers and passwords, to us via ordinary (unencrypted) e-mail.