Hi
Great question, but it's really hard to answer without knowing what service you provide. Also, it really depends what percentage your talking about - if its low - I wouldn't waste time on it for now.
I myself have personally wanted to use an online service which claimed to be free, and the sign-up deterred me so I just gave a wrong email address. If it's a once-off action on behalf of the user (for example converting a file), users are lazy and even something like giving their email deters them.

I am happy to solve this issue with you, but I would need to get more details, following which we could have a short call to discuss the conclusions.
Good luck

A few possibilities. And, as noted already, if this is a tiny percentage that's not impacting your business you could ignore it.

1. They're spam sign-ups. Have you noticed a wildly unrealistic uptick in overall traffic? You could be getting throttled by bots.

2. There's a problem with your email sender score, so your emails aren't getting through spam filters. What's your deliverability percentage?

3. There's a problem with the email itself:
-> subject line issues decrease open rates or can decrease clicks if there's disconnect between open and what the recipient actually finds inside
-> copy or design issues can cause clickthrough issues

4. There's a disconnect between what people expect when they sign up and what they have to do when they get that email. Do they know they're going to get the email? Is it worth the time for them to take that next step, depending on what value they expect to get from the sign up?

Great question!

This potential issue is actually a good opportunity for you to sign up as a fake user (just add your email and information exactly how a normal email recipient would) and test the process end-to-end.

It is easy to have something small break as you have spent a lot of time, I'm sure, developing the detailed process. Take a step back and ensure the whole process is smooth and there are no potential for the email to break.

After this is confirmed, I would dig deeper into the analytics. What industry are you in? What are you looking at? Are these the right consumers for your market? All of these questions will help you get to an answer as to what the issue truly is.

If that doesn't work, the last step would be to send them an informal email (likely from another inbox at the same domain) and just ask the person for candid feedback. Often times customers will tell you everything you could have ever wanted to know, from a simple email.

I would love to work with you to get to the root cause of this issue and to help your business. Let's setup a call to discuss all the details!

There can be several reasons why people may be unable to verify you email. Most common are that these emails land in their spam inbox and get deleted. Other reason can be that they feel that you are trying to scam them, so they ignore it all together. Other reasons can be they find the email attractive enough to act, they might have been attracted to your website, but the email wordings may not be attractive enough. One of the worst mistakes you can make with your email marketing is to simply blast every subscriber on your list with the same message. Using list segmentation to send the right message to the right audience is critical to success with email marketing. Not to mention that when you are dealing with serious topics like health-related information, blasting the same content to all your users can have some bad results. List segmentation is simple to do.
You can read more here: https://www.forbes.com/sites/gabrielshaoolian/2017/05/10/6-ways-to-improve-your-email-marketing-campaigns-and-boost-sales-online/?sh=2088689362f0
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath