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copied!<p>An email address must not exceed <strong>254</strong> characters.</p> <p>This was accepted by the IETF following <a href="http://www.rfc-editor.org/errata_search.php?rfc=3696&eid=1690" rel="noreferrer">submitted erratum</a>. A full diagnosis of any given address is available <a href="http://isemail.info/" rel="noreferrer">online</a>. The original version of RFC 3696 described 320 as the maximum length, but John Klensin subsequently accepted an incorrect value, since a Path is defined as</p> <pre><code>Path = "<" [ A-d-l ":" ] Mailbox ">" </code></pre> <p>So the Mailbox element (i.e., the email address) has angle brackets around it to form a Path, which a maximum length of 254 characters to restrict the Path length to 256 characters or fewer.</p> <p>The maximum length specified in <a href="http://tools.ietf.org/html/rfc5321#section-4.5.3" rel="noreferrer">RFC 5321</a> states:</p> <blockquote> <p>The maximum total length of a reverse-path or forward-path is 256 characters.</p> </blockquote> <p>RFC 3696 was corrected <a href="http://www.rfc-editor.org/errata_search.php?rfc=3696" rel="noreferrer">here</a>.</p> <p>I've now collated test cases from Cal Henderson, Dave Child, Phil Haack, Doug Lovell and RFC 3696. 158 test addresses in all.</p> <p>I ran all these tests against all the validators I could find. The comparison is here: <a href="http://www.dominicsayers.com/isemail" rel="noreferrer">http://www.dominicsayers.com/isemail</a></p> <p>I'll try to keep this page up-to-date as people enhance their validators. Thanks to Cal, Dave and Phil for their help and co-operation in compiling these tests and constructive criticism of my own validator.</p> <p>People should be aware of the <a href="http://www.rfc-editor.org/errata_search.php?rfc=3696" rel="noreferrer">errata against RFC 3696</a> in particular. Three of the canonical examples are in fact invalid addresses.</p>

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