why are special character not alloed in email address

I was just curious about why only a few special character are not allowed in email address. Except a few special character like ".", "_" etc most of special character characters bot allow开发者_StackOverflowed. is this a technology constraint or just a convention without any reason ?

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It's a blatant falsity that is unjustly imposed by overzealous email regexps.

Almost all characters can be used in email addresses.
"abc def+ghi/jkl@mno*pqr"@localhost is a valid email address.

Even without quoting, !#$%&'*+-/=?^_`{|}~@hi is valid.

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Check RFC-2822 for details on the specification of internet email addresses.