Valid email defination

https://help.returnpath.com/hc/en-us/articles/220560587-What-are-the-rules-for-email-address-syntax-

For an email to be delivered, it must have a valid address that follows certain rules of syntax.

A valid email address has four parts:

• Recipient name
• @ symbol
• Domain name
• Top-level domain

Recipient name
The recipient name represents an email mailbox that belongs to:

• A specific person
• A mailing list
• A department
• A role within a company (such as sales or customer service)

The recipient name may be a maximum of 64 characters long and consist of:

• Uppercase and lowercase letters in English (A-Z, a-z)
• Digits from 0 to 9
• Special characters such as ! # $ % & ' * + - / = ? ^ _ ` { |