Whether you have 500 contacts or 5000 contacts on your email list, it is irrelevant.
The focus isn't on building the list; it is about creating engagement.
What's the best way to see if you have an engaged list?
Send them an email with a link for more information.
Contacts that are engaged will click the link.
Don't think that having an above-average open rate means your emails are working.
You need to measure your engagement by click through rates.