When a posting is sent out, any users whose e-mail as been blocked, end up with a log entry with the "action" set to "mail blocked". When checking the list of course participants afterwards, each person whose mail has been blocked is displayed as having last logged in at the time that the forum posting was sent.

In fact, two entries appear in the log for each blocked message. Both of the URLs are those of the site where the crontab resides (my school, in this case) although the site is located on an ISP provider in the U.S.