Could we consider it as a security flaw to not ask an email verification on account creation?
Let's say there is a service that ask you to enter an email address as a username and a password in order to create an account. Then, as soon as you press the "create account" button, your new account is ready and you're never asked to verify your email address.
The first thing that comes to mind is that you won't be able to get back this account if you don't own the email address, but is it also possible to exploit the fact that there is no email verification to deny possible users to the service?
For example, if I own a competitor company, I could create account using the email of my clients on that other company website and I would effectively block those clients from creating an account using their favorite email address for that other company.
It's just annoying to the user to try to create an account and realize that your own email address is already taken while you have clearly not created an account, but, on the web, anything that annoy your users will make you lose customers.
I'm asking that question because I believe a previous question got misunderstood and I'm assuming in the other question that this is a problem. So please, help me understand whether or not this is an issue.