Valid characters in both the username and domainname part are limited to ASCII, excluding the following characters:
Mail addresses should rarely be considered authoritative, because of the nature of SMTP it is very straightforward to forge an address or enter an invalid address when connecting to a server. This is most commonly seen when dealing with spam messages. If security is required, messages should be digitally signed or encrypted.
Having your own e-mail address is considered an essential part of life in cyberspace and is required for almost everything other than viewing pages. Making online purchases, subscribing to paid content, posting in web logs or Internet forums, participating in Usenet newsgroups and many other tasks will require a valid e-mail address. Despite once being considered part of "geek culture", not having an e-mail address can seriously disadvantage a person. For this reason, many governments in modern countries are undertaking initiatives to give e-mail addresses to public servants and school children.The Need for E-mail