email lists

I have some emails on my mailing list that are from 2016 and I was wondering if I should keep them or delete them after some time. My email list is really small right now so I was thinking I should keep them but I don't know if that is a good practice or not.

I saw something on a blog that said that contests can be a good way to attract attention to something. Are contests good for building our email lists or are they better for other uses?

I have something that I want to try out and I am thinking about buying an email list. I have never bought one before and have always built my own lists because I want a quality list and not basically a universal list that sellers will say is good for this niche or that niche. So, based on what...