welcome to the forum!
I've been working in sign-up and onboarding flows for a few years and in my experience there are many ways to address the problem you are describing depending on what part of the equation you want to focus on.
One (sort of) simple solution here is to check the email structure and trigger a reCaptcha v3 when the email looks suspicious.
The caveat is that some bots eventually learn how to bypass these verifications and also, for those users who get mistakenly detected as spam you are adding an extra point of friction. This friction though can potentially make up for the loss in email confirmations.
Lack of engagement
This one is a fun one because you can pretty much do whatever you want. Depending on the nature and tone of voice of your platform you could try adding some fun element or even gamification to the sign-up process by telling the user something like…
Thank you for signing up to ACME Ind!
We just sent one of our best elves to your email to verify your account. Treat him well, he is a bit shy.
Before getting into the solutions I described above, you should probably analyse the current performance of your first email and the reminders. Consider the following:
- What's the Open Rate of the first email?
- From those users who open a reminder, what's the average time they need to confirm the account? Is it after the 1st reminder, the 2nd… ?
- What's the average Click Through rate of those who open the email? In other words, how many users of those who open the email end up confirming the account?
- How many clickable elements you have on that email?
- Have you experimented with the subject line? I recommend making the subject line relatable and personal by using the $firstname token.
- Is the design of the email clear, clean and visually engaging?
- Have you checked if your email is falling under spam and in what percentage of the cases?
After you have analysed all of those aspects you should have a good set of data to start making assumptions and defining possible solutions to confirm them.