It seems spam has been on the rise lately and overwhelming by one clever clown.
This spammer relays mail servers and has must have a list of e-mail address for these servers. The subject is slightly changed with each e-mail which makes filtering on it difficult.
Subject similar to: halbo
After looking at headers between e-mails sent, no IPs matched. The only header that was consistent is as follows.
X-evolution-source: 1287898080.4201.30@Laptop
Creating a filter on this header has allowed me to flag these messages to be deleted on receipt. (10 - 20 a day)