That sounds like a broken auth situation, if the email is the exact same. There’s gmail workaround where you can put sam+Test1@gmail.com and then sam@gmail.com and it would technically be one address in Gmail, but a site would see that as two separate addresses.
The question would be what would be the impact of having two accounts with the same email address. Some websites allows authentication via username, and uses email just for communication or password resetting of accounts. This behaviour would be intentionally done.
If it can be used to take-over an account for example or disallowing a user from using his account, then it would be an issue in my opinion.
There are cases in which this can turn out as a malicious action. Under certain conditions, databases may or may not inform the application that this e-mail address exists, therefore overwriting the previous record and usually taking over the account.