电子邮件地址格式的正式定义是什么？

Question

我想知道构建电子邮件地址的正式定义。

我不仅仅想要答案，而是如何实现答案，因为我将学会如何自己做。

Answer 1

正式定义？请参阅RFC821。

<path> ::= "<" [ <a-d-l> ":" ] <mailbox> ">"
<a-d-l> ::= <at-domain> | <at-domain> "," <a-d-l> 
<at-domain> ::= "@" <domain>
<domain> ::=  <element> | <element> "." <domain>
<element> ::= <name> | "#" <number> | "[" <dotnum> "]"
<mailbox> ::= <local-part> "@" <domain>
<local-part> ::= <dot-string> | <quoted-string>
<name> ::= <a> <ldh-str> <let-dig>
<ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>
<let-dig> ::= <a> | <d>
<let-dig-hyp> ::= <a> | <d> | "-"
<dot-string> ::= <string> | <string> "." <dot-string>
<string> ::= <char> | <char> <string>
<quoted-string> ::=  """ <qtext> """
<qtext> ::=  "\" <x> | "\" <x> <qtext> | <q> | <q> <qtext>
<char> ::= <c> | "\" <x>
<dotnum> ::= <snum> "." <snum> "." <snum> "." <snum>
<number> ::= <d> | <d> <number>
<CRLF> ::= <CR> <LF>