The total for the "spam" category is the sum of messages that are received by my mail server but get no further. In this category are messages that my spam filters immediately delete on the server, plus suspect messages that are placed in a special server directory for manual inspection. The manual inspection process is of the raw mail file in text mode, without bringing any of those messages down to my personal computer's email client program. In this total are the rare good mail message that may be inadvertently deleted, and the one or two per week that find their way into the "suspects" category. Not in this total are a daily average of about 10 unwanted messages that make their way through my filters to my email client.
The category "virm" includes viruses, worms, and Trojans that attempt to reach me via email. The total for this category is a count of all messages that my server filters tag as being of a viral nature and then promptly delete on the server. Not counted in this group are the messages that have had their viral payloads removed by the sending server or ISP and then find their way into either the "spam" category, or are harmlessly (but annoyingly) delivered to my client.
The problem of massive dictionary attacks against my domain started only in 2004, but has earned itself its own measurement category. The count for this category is the number of attempts to connect with my mail server that are summarily rejected because the message is directed at an invalid address on my server. This includes not only true dictionary attacks, but corrupted variations of good addresses that have propagated among spammers' address lists for years. (Note: Due to the disproportionately high number of these items compared to others in the chart, the yellow bars are scaled down by a factor of 10. The numbers in the textual chart represent the actual amounts.)
An SMTP-AUTH attack is someone (some computer, really) trying to use my mail server to relay messages, but failing to do so because they don't know my server password.
The spam rate is a calculation of what percentage of all mail that is received by my mail server is unwanted garbage. In other words, when you see a spam rate of something like 98%, it means that only two percent of the day's received messages were things I wanted to receive.