Hah, I did something sorta similar in my freshman year of high school - I noticed that emails sent to the whole school were sent to mailing lists (in gmail's terminology - not sure what this kind of address is in actual email standards) called "allYYYY.student.school.org", where YYYY is the graduation year of a grade and student.school.org is the domain all our student emails were at. I hadn't seen that kind of email address/mailing list address before, so I wondered whether it was just a legit email address as well. It turned out it was (it was for a google group in the domain also called "allYYYY" IIRC) so when I sent an email with subject line "Hello" and body "?" to allYYYY(at)student.school.org to see if it would give me a mailer daemon response, that got sent to all ~800 people in my grade, some of whom promptly started replying to all. Eventually a couple kids started sending edgy memes, so I was called into my dean's office and asked to forward them the whole thread so that they would know they weren't missing out on anything "dangerous" (I think the main one they were concerned about was a picture of someone shooting a gun with the caption "I would literally die if a guy did this to me"). Then they locked down the capabilities on the google group, so no more unapproved email campaigns :(