How can I determine the relationship between spam and weekdays?
(started as a comment but it turned out to be longer than expected)
With a dataset like this a simple barplot could be very insightful: on the X axis the days of the week, on the Y axis the frequency, with two bars (spam/not spam using different color) for each day. A slightly more advanced version: two boxplots, one for weekdays the other for weekends. A boxplot is kind of overkill for only 5 (mon-fri) and 2 (sat-sun) values but it's easy to do and shows the big picture.
In order to test whether any difference (e.g. weekdays vs weekends) is significant I think this is a good case for a chi square test.