Should I delete inactive users from my “newsletter” email list to keep my email marketing service fees down or continue to send these users emails?

Don't delete them: segment them. Move them to another list for their own retention campaign. Send them a series of 3 messages saying that you've noticed that they haven't read anything from you lately, and you want to make sure that they're still interested in receiving information from you. If after that, you still haven't heard from them, delete them. In addition to keeping your costs under control, it will also improve your open/click rate with your sender, which, depending on which service you use, may be important, as it's often taken into consideration if you get a lot of unsubscribe requests or spam reports.

Let me add to Scott Allen's sound direction...

The odd answer is Yes to both, let me clarify:

1. You sent an AR sequence to 3 types of audiences - you should have 3 for those who take action initially (open/click), those who take action more than once (visit your web site, open/click more than once), and those who never open/click.

One AR sequence doesn't fit all; you need to craft 1 new one to keep your list clean.

2. Focus on those who never open/clicked over 30, 60, and 90 days. See what numbers come up, and send an onboarding or leave sequence.

My tests for email dev show a 3 month window, but those are my lists/market. If you have volume, cleaning your list is critical.

3. After 90 days, the lead value goes down, descending from 2 weeks to 30 days, when most lose value. With a focused approach, you can convert a portion of those over time.

I've added 5-10% to my lists, while cleaning 20-30% so I don't over clean.

Yes you need to email them and yes delete them, and not just to keep costs down. This will be one of the many steps to improve your deliverability with low bounces, low unsubs, and improved open/click rates.

Hope this helps,

A few things came to mind when I read this post:

1) Have those email addresses been verified to make sure those are not spam/fake addresses?

2) Why do you think are these customers not converting? Were the emails catered to the needs/interests of these individuals? Are they just not interested?

3) How long has it been since you last followed-up?

If you cannot manage it, it is advisable to delete some of the users. It is impossible to get everyone to read your emails, but you can improve the chances of customers reading them if you feel you cannot do that, there is no point in keep them.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath