EmailField? does not comply with SMTP standard

[qqq1one@…]

Email addresses in the literal form (where the square brackets are included):

user@[123.123.123.123]

are indicated as invalid by EmailField.

But the literal form is valid as per section 4.1.3 of the SMTP standard:

Sometimes a host is not known to the domain name system and
communication (and, in particular, communication to report and repair
the error) is blocked. To bypass this barrier a special literal form
of the address is allowed as an alternative to a domain name. For
IPv4 addresses, this form uses four small decimal integers separated
by dots and enclosed by brackets such as [123.255.37.2], which
indicates an (IPv4) Internet Address in sequence-of-octets form.

Reference: ​http://tools.ietf.org/html/rfc2821#section-4.1.3

Also referred to in ​http://tools.ietf.org/html/rfc1123#page-57:

5.2.17 Domain Literals: RFC-822 Section 6.2.3

A mailer MUST be able to accept and parse an Internet domain
literal whose content ("dtext"; see RFC-822) is a dotted-
decimal host address. This satisfies the requirement of
Section 2.1 for the case of mail.

An SMTP MUST accept and recognize a domain literal for any of
its own IP addresses.

[trez]

Tests are ok.

[Luke Plant]

In [16355]:

Fixed #16166 - EmailField does not comply with SMTP standard

Thanks to qqq1one@… for the report, and samufuentes for the patch.