This document provides information on email address formats and restrictions. It explains that an email address has two parts separated by an @ sign, with the local part allowing 64 characters including some special characters, and the domain part allowing 255 characters following hostname requirements. It also provides a sample regular expression that checks the format but has some exceptions for valid addresses it does not pass.

1. https://www.fraudlabspro.com/

2.  An email address must comes with two parts separated by an at-sign (@), namely
the local part and domain part.
 The characters allowed in both parts are different based on several conditions and
restrictions.

3.  The local part can contain up to 64 character and also contain some special
characters without any restrictions:
 Any special character that are not listed, should be used in the quotes.
 For example,
 Be in mind that the period sign (.) can be used in local part with the following
restrictions:
! # $ % & ‘ * + – / = ? ^ _ ` . { | } ~
 Abc@def@example.com
 Fred Bloggs@example.com
 Not in the first or last of the local part
 Cannot be used consecutively.

4.  The length of domain part has up to 255 characters
 It must follow the requirement for hostname and a list of dot-separated DNS
labels limitation of 63 characters length with the requirements of:
 Note: The dotless domain name(xxx@example) is prohibited by the Internet
Corporation for Assigned Names and Numbers(ICANN) due to security and
stability risks.
• uppercase and lowercase Latin letters a to z;
• Number digits 0-9, with the condition of top-level domains cannot be all
numeric;
• The hypen symbol(-), provided that it should not be the first or the last
character.

5.  Below is the sample of regular expression:
 This regular expression will first check the first character in email address if the
double quote found, it will make sure the character embraced inside the double
quote is valid as according to the standard.
/^([!#-'*+/-9=?A-Z^-~-]{1,64}(.[!#-'*+/-9=?A-Z^-~-]{1,64})*|"([]!#-[^-~
t@]|([t -~]))+")@([0-9A-Z]([0-9A-Z-]{0,61}[0-9A-Za-z])?(.[0-9A-Z]([0-9A-Z-
]{0,61}[0-9A-Za-z])?))+$/i

6.  There are some exception cases. For example, the following cases will not pass the
regular expression checking although it’s correct.
 “test”test”@example.com
 “test”.”test”@example.com
 “test”.test@example.com
 “test”@example.com
 “test”@example.com
 Please note that although RFC standards allows the use of IP address in domain
part, but this is not cover in this regular expression checking.

7. https://www.fraudlabspro.com