Is it possible still to find some mailing lists that are active? I can't think of many active social or general-purpose mailing lists, because this traffic has largely gone elsewhere, as you say. However, I find that for me, participating in active topical mailing lists (like the analogue heaven mailing list for analog synthesizers) can cheer me up, because it's very functional discussion where if I have something useful to add, I feel like I'm helping out. That's actually what works best when I'm feeling depressed for me -- opportunities where I can feel like I've been useful or helped someone out.