Fixing that requires a fancier kind of validation that involves sending that address a message that includes a confirmation token meant to be entered on the same web page as was the address.Д¬onfirmation tokens are the only way to know you got the address of the person entering it. People sign others up to mailing lists this way all the time. It's also important to understand that validating it per the RFC tells you absolutely nothing about whether that address actually exists at the supplied domain, or whether the person entering the address is its true owner. However, if you are forced to use one of the many less powerful pattern-matching languages, then itвЂ™s best to use a real parser.

Python and C# can do that too, but they use a different syntax from those first two. in PHP) can correctly parse RFC 5322 without a hitch. The more sophisticated patterns in Perl and PCRE (regex library used e.g. (Scrape the rendered version, not the markdown, for actual is diagram of finite state machine for above regexp which is more clear than regexp itself The rest of it appears to be consistent with the RFC 5322 grammar and passes several tests using grep -Po, including cases domain names, IP addresses, bad ones, and account names with and without quotes.Д¬orrecting the 00 bug in the IP pattern, we obtain a working and fairly fast regex. One RFC 5322 compliant regex can be found at the top of the page at but uses the IP address pattern that is floating around the internet with a bug that allows 00 for any of the unsigned byte decimal values in a dot-delimited address, which is illegal. RFC 5322 leads to a regex that can be understood if studied for a few minutes and is efficient enough for actual use. Fortunately, RFC 822 was superseded twice and the current specification for email addresses is RFC 5322. The fully RFC 822 compliant regex is inefficient and obscure because of its length.

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