About 15 plus years ago I emailed my customer list with a sale and it cause me issues with my email coming up as spam. For a couple of years after my emails would end up in people spam boxes. Literally since then I haven't tried this again. But I think its time to try again.

I was wondering if mailchimp is a good way to avoid this or any other tips people may have?

What I did was purchase a different domain name to send email campaigns from to avoid this very thing (blacklisting your primary domain).
Domain names are cheap.
So if your domain names is www.widgets.com you might get the domain www.widget-news.com for example.
The idea is customers still recognize the domain or company name.

This has worked for me.

Good idea, thanks!