Syntax
The format of email addresses is local-part@domain where the local-part may be up to 64 characters long and the domain name may have a maximum of 253 characters – but the maximum 256 characters length of a forward or reverse path restricts the entire email address to be no more than 254 characters. The formal definitions are in RFC 5322 (sections 3.2.3 and 3.4.1) and RFC 5321 – with a more readable form given in the informational RFC 3696 and the associated errata.
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