Confused about Platform

I have a personal blog that's been live for a couple of years, but I've only posted a couple of times. Somehow, I have an email subscriber list of 315. Most of them popped up after I added a link to my blog on my Cloudveil/Telegram profile. I was really excited, and sent an email when I created a new post, but probably at least 200 of the email sent out just bounced. How can I tell whether a bunch of them are bots or hackers, does that ever happen? On the other hand, if they're real, I sure don't want to delete them!

Also, does anyone have tips for engaging an audience before you have anything published? I don't want to get a bunch of readers excited, only for their kids to grow up, and suddenly they're no longer interested in my picture books!