June 30th, 2003, 12:36 AM
What makes an email valid
Google searching gives me a bunch of premade email validators, and a few rules. If i examine the regular expressions in most email validators, I can extract a set of rules, but somewhere along the line someone must have had a document with the set of rules.
I did look through RFC's 821 and 2822, did find section 3.4 Address specification but that did not seem to give me the rules for valid email.
I discovered, that username@ip-address is valid but not acepted by many sites. I came across a usenet post, and it was stated whatever sendmail acepts is valid, but we know sendmail is not the only mail deamon.
In my Google searches I did come across some rules.
Valid characters are a-z 0-9 hiphen, underscore and dot. Must be at least 7 characters, can contain only one @. Extension (.com, .net...) can be 2 to 4 characters, . and @ cannot apear together. sub domain must have at least 2 letters. No spaces are alowed.
Can someone please direct me.
June 30th, 2003, 02:05 AM
I noticed that too, I went to sign up with http://myip.us/ and they told me i was useing an anonymous email and I cannot use hotmail, yahoo..other emails that are anonymous, and that my isp email would work,
Id come across a email validator the other day that after validating the format, did a rDNS check on the domain to verify it exists. My idea is to extend this by also doing a finger, so if it is a registered isp email acount I should be able to get the finger information if the user realy exists.
Thanks for your responce
June 30th, 2003, 09:10 AM
Most (smart) isp's won't allow you to finger them !!
but there are other sollutions, including googleing the email adress, that gives and indication of the validity too. .
So a blacklist of email hosts (hotmail msn yahoo etc.) in combination with a rDNS and some other stuff might do the trick..
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June 30th, 2003, 09:27 PM
Thank you the_JinX for that tip. I did notice hotmail does not respond to a finger, but didnt realize some isps dont either. I can see why though, as a security feature.
Just learned that php has a rdns, checkdnsrr that can check to see there is a MX record for the host in question. And that it is not suported in the windows version of php, so now im looking into a command line utility nslookup and to make my own checkdnsrr function.