I work with lots of clients who spend a lot of time and energy on their Facebook advertising & their Instagram accounts (with varying success) but have a list of people gathering dust in their Mail Chimp account.
Yes it can take more time and effort than pushing "Boost" on a post but when people have expressed interest in your products or services, your time will likely have a higher return if you focus on those people.
Consider How People Interact With Email
Think about how you interact in your email compared to how you might interact with an ad on Facebook. Sure, everyone will be different but in most cases when you've signed up for a newsletter (and not just to enter a contest) you will pay attention to it when it arrives in your inbox.
Even when there's lots of emails vying for my time, I know that when I read my Marie Forleo emails I am left feeling uplifted and inspired, so I will open those nearly every time. However, because a lot of my work is done on Facebook, when I am on that account I am focused on the task at hand so I don't know if I've ever clicked an ad there.
I know that I may not be an average user on Facebook but the platform itself is built as a tool for distraction so the mindset of someone using it varies compared to a person looking at their emails.
Set a Schedule and Send Your Newsletter
If your business has a list of people who have willingly signed up to your newsletter (and they should always willingly do so, no sneaky stuff!) then don't ignore those warm leads. Find a rhythm, set a schedule and make sure you're sending out newsletters! Even if it's just quarterly.
To make it easier, set up a template for yourself with a space for a short update, a place to feature your newest product or project and any blogging you might be doing. (Read about why a blog helps your website rankings.) That way, all you're doing each time is filling in the placeholder areas with your information.
Track the Results
If you have an ecommerce site, make sure you have all of the tracking setup to measure the sales you get out of a newsletter. This can be enough encouragement to keep up your sending in some cases!
Other useful metrics are which links get the most clicks. This will give you a good idea of the kind of content to include so that you are driving people to your website with each send. Don't get too hung up on open rates (especially if you haven't sent for a while...) as every list will have different behaviour. Review your average after a few newsletters have gone out to get a sense of what good performance means for that list in particular. (I was talking to someone who was unhappy with an 80% open rate but I will tell you that should be considered a great success!)
Keep it Clean
Don't forget to clean up your list regularly. There's no sense emailing someone who never opens any of the messages - especially if you are paying to send to them. Most email marketing platforms let you run reports on the subscriber activity which will help you identify who is engaging and who can be taken off the list. Check up on it a few times a year at least - of course, make sure you have activity to measure against though!
If you need help with your email marketing, get in touch. Otherwise, if it's just a matter of making the time, then get on to it!