What is an ok rate on unconfirmed emails?

We are running an online platform which requires a signup from the user. After completing the signup flow, the users is prompted to confirm her email. Without confirmation, the users can't use the platform.

Everyone can signup, only an email is required. The platform is for online volunteering for creatives from the spaces design, communication and tech. So I assume that every user has a goal while signing up.

Since the start 4 years ago we are monitoring a stable rate around 20% of the users which are never confirming their email (around 4% of the emails are bouncing). We thought hard about this and came to the conclusion that the 20% includes users

  • which entered a fake email (why should a user do this?)
  • made a spelling mistake
  • doesn't have access to email account anymore (why should I use an email to which I don't have access?)
  • signed up on mobile and doesn't have mobile email access, thus never finishing the sing up (are users really forgetting things so fast?)

In generell we are really unsure if 20% is ok and what the real reasons are. Anyone here to share some wisdom? :) Cheers, Lars

PS.: We once put a nice illustration on the confirmation page which decreased the bounce rate by 1,3% - yeah!