Although the standard requires the local-part to be case-sensitive,[1] it also urges that receiving hosts deliver messages in a case-independent manner,[2] e.g., that the mail system in the domain example.com treat John.Smith as equivalent to john.smith; some mail systems even treat them as equivalent to johnsmith.
The local-part of an email address has no significance for intermediate mail relay systems other than the final mailbox host.
Email senders and intermediate relay systems must not assume it to be case-insensitive, since the final mailbox host may or may not treat it as such.
Email aliases, electronic mailing lists, sub-addressing, and catch-all addresses, the latter being mailboxes that receive messages regardless of the local-part, are common patterns for achieving a variety of delivery goals.
[citation needed] RFC 5321 also warns that "a host that expects to receive mail SHOULD avoid defining mailboxes where the Local-part requires (or uses) the Quoted-string form".
Indeed, RFC 5321 warns that "a host that expects to receive mail SHOULD avoid defining mailboxes where ... the Local-part is case-sensitive".
For example, Windows Live Hotmail only allows creation of email addresses using alphanumerics, dot (.
[16] Addresses of this form, using various separators between the base name and the tag, are supported by several email services, including Andrew Project (plus),[17] Runbox (plus),[18] Gmail (plus),[16] Rackspace (plus), Yahoo!
[29][30] The text of the tag may be used to apply filtering,[27] or to create single-use, or disposable email addresses.
[31] The domain name part of an email address has to conform to strict guidelines: it must match the requirements for a hostname, a list of dot-separated DNS labels, each label being limited to a length of 63 characters and consisting of:[9]: §2 This rule is known as the LDH rule (letters, digits, hyphen).
RFC 2606 specifies that certain domains, for example those intended for documentation and testing, should not be resolvable and that as a result mail addressed to mailboxes in them and their subdomains should be non-deliverable.
An email address is generally recognized as having two parts joined with an at-sign (@), although technical specification detailed in RFC 822 and subsequent RFCs are more extensive.
For example,[34] Some companies offer services to validate an email address, often using an application programming interface, but there is no guarantee that it will provide accurate results.
EAI enables users to have a localized address in a native language script or character set, as well as an ASCII form for communicating with legacy systems or for script-independent use.
Applications that recognize internationalized domain names and mail addresses must have facilities to convert these representations.
Significant demand for such addresses is expected in China, Japan, Russia, and other markets that have large user bases in a non-Latin-based writing system.
For example, in addition to the .in top-level domain, the government of India in 2011[39] got approval for ".bharat", (from Bhārat Gaṇarājya), written in seven different scripts[40][41] for use by Gujrati, Marathi, Bangali, Tamil, Telugu, Punjabi and Urdu speakers.
Indian company XgenPlus.com claims to be the world's first EAI mailbox provider,[42] and the Government of Rajasthan now supplies a free email account on domain राजस्थान.भारत for every citizen of the state.
[43] A leading media house Rajasthan Patrika launched their IDN domain पत्रिका.भारत with contactable email.