The regular expression include the following:
Local part include (at least 2 characters):
1. Uppercase and lowercase English letters (a-z, A-Z)
2. Digits 0 through 9
3. Characters ! # $ % & ' * + - / = ? ^ _ ` { | } ~
4. Character . (dot) provided that it is not the first or last character, and provided also that it does not appear two or more times consecutively.

Top Level Domains include:
1. country-code top-level domains (ISO 3166)
2. generic top-level domains
3. sponsored top-level domains
4. infrastructure top-level domain

Detailed Discussion will be found: The regular expression for checking email