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Any standard for Email address?

Is there any specific standard to an email address?  How can I check if the email address entered by the user is correct?
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christayec
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christayec
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ReCompileCommented:
the standard for email addresses is Username@domain-name.  The only way I can think of to verify if the email address is correct is to verify that it is in that basic format.
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tfabianCommented:
the proposed answer isn't entirely accurate..

there is no "standard" format for email addresses..   sure most of them at in the format of userid@host.in-domain as "ReCompile" suggestted, but many places are also using firstname.lastname@domain instead coupled with x.500 gateways that end up routing to the final machine destination.. in doing so, it's a cleaner, more secure environment.. you end up not having to advertise all your machine names to the world, and thus they're more secure since potential hackers don't know about them..


anyway, getting back to the discussion, the format for email addresses really depends on the organization that issues them, whether or not they use an x.500 gateway, or x.400 addressing standards, and what their primary email software is based upon..

eg. if you used a DEC ALL-IN-1 email system with an SMTP gateway, your address might look like

    smtp%"JOHN_SMITH@A1"@host.domain

while if you were on a unix system directly connectted to the network and processing SMTP itself, it might be something like

   jsmith@host.domain


or if you relied on x.400, it might be

 /fn=John/sn=Smith/o=Org-Code/@x400-gateway.domain


or if you relied on x.500, it might be

   John.Smith@domain


all are potentially valid depending on the circumstances and systems involved..

as for checking on the validity, there are two or three ways..


1)  send mail to the address and see if it bounces back to you..

2)  telnet to port 25 of the host named, and issue the VRFY command to see if
     the ID exists... it should tell you if the account is valid...

 3)  finger the address.. if it exists, the host should return a message telling you so..

4)  call up the company / isp of the domain, and ask them to verify the address...



but beyond that, there isn't a good way to check on validity of an email address... I wish there was...



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tfabianCommented:
since OZO brought up RFCs, I might as well add that the RFC he references has been updated by RFCs 1123, 1138, 1148, 1327, and 2156...


you can find all the RFC online at url  http://sunsite.auc.dk/RFC/main.html


RFCs are de facto standards documents, but by their nature, ie. RFC stands for "Request For Comments", they are only valid until someone writes a new one and updates or obsoletes an old one..

if you want to play the game of "meeting a standard" the generally agreed upon standards are the relevant RFCs...


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