What is domain verification?
Domain verification has good intentions, but can sometimes cause issues with good people. The registry will send an email to the domain registrant, asking them to verify their email address. By doing so, it assures the registry that there is a person behind the email address and not a hacker simply owning a domain with a fake email address. If you do not reply to the email, the registry thinks you are simply not a live/real person and suspends the domain in the attempts to combat bogus registrations.
This went info effect January of this year and applies to all domains whether they have already been registered for some time or have been newly registered. Domain verification is also triggered when you change the email address associated with a domain to prevent users from first registered with a valid email and then changing it to a bogus address, breaking the chain of contact.
Once your email address is verified, it will cover any/all domains within the entire registry so you only have to do it once per email address.