You are not really failing for WCAG 3.3.3
3.3.3 Error Suggestion: If an input error is automatically detected and suggestions for correction are known, then the suggestions are provided to the user, unless it would jeopardize the security or purpose of the content. (Level AA)
This point means that you can provide a suggestion. For instance, the user type "user AT example.com" and you suggest "Do you mean user@example.com?"
Here, you fail for WCAG 3.3.1:
3.3.1 Error Identification: If an input error is automatically detected, the item that is in error is identified and the error is described to the user in text. (Level A)
You have to describe the error in plain text which means "Enter a valid e-mail address (example: user@domain.com)".
And you might also be concerned by 3.3.2, which is the lack of instructions
3.3.2 Labels or Instructions: Labels or instructions are provided when content requires user input. (Level A)
which means that if a label is not sufficient, you have to give instructions (valid format).
Note that things might be different when you use the browser self validation process for the HTML5 input[type="email"]
element. Because there, the browser Accessibility API should provide an explicit error message.