Validating forms using html5
The MTA next connects to this server as an SMTP client.The local part of an email address has no significance for intermediate mail relay systems other than the final mailbox host.With the introduction of internationalized domain names, efforts are progressing to permit non-ASCII characters in email addresses.The transmission of electronic mail within the Internet uses the Simple Mail Transfer Protocol (SMTP), defined in Internet standards RFC 5321 and RFC 5322, and extensions like RFC 6531.For example, Windows Live Hotmail only allows creation of email addresses using alphanumerics, dot ( 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:, although this is rarely seen except in email spam.Internationalized domain names (which are encoded to comply with the requirements for a hostname) allow for presentation of non-ASCII domains.Some mail services support a tag appended to the local-part, such that the modified address is an alias to the unmodified one.For example, the address joeuser [email protected] the same delivery address as [email protected]
In some cases they also limit which addresses it is possible to send mail to.
A quoted string may exist as a dot separated entity within the local-part, or it may exist when the outermost quotes are the outermost characters of the local-part (e.g., specify different mailboxes; however, many organizations treat uppercase and lowercase letters as equivalent.
Indeed, RFC 5321 warns that "a host that expects to receive mail SHOULD avoid defining mailboxes where ... Despite the wide range of special characters which are technically valid, organisations, mail services, mail servers and mail clients in practice often do not accept all of them.
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.
A single mailbox may receive mail for multiple email addresses, if configured by the administrator.