I'm also curious to hear if/when you think sending an email to all students is a bad idea, or if other ways to reach people might be more effective. I recently worked with Jack Ryan, Nikola Jurkovic, and a few others to send an email to MIT and Harvard students, but I'm curious to hear others' thoughts and don't want to anchor people. I'll add our email after a few days. (I also realize I should've probably asked around before sending our email, but we were pressed for time).
Perhaps this goes without saying, but please also (strong) upvote ideas based on how good you think they are, and explain why.
We did get a lot more fellowship signups and engagement that semester than previously, but I'm pretty sure we would have gotten more fellows/engagement even if the aforementioned email had been different or hadn't existed, since a co-organizer and I put a lot more energy into my college's EA group that semester than it had previously received, including other advertising. So I have no idea how much of the effect to attribute to that email. (But looking back, I still think that email was a good one.)