Url and email validation

Anon

Hello

I am working on url and email validations (not again i hear)

can anybody help with domain names and url formats I am trying to find the limitations of a url.
i.e howmany character maximum , minimum
how many dots, hyphens, how many groups

i.e fred.fred.fred.fred is this valid
is fred.fred.fred.fred.fred valid
(fred is just a string of character)
and domain names is there a limit to the length

and for email addressses
does any body know
the maximum length in front of the @ sign

Any help or pointer geatly appreciated.
Mark

theslinky

I believe domain names can be 64 characters long, but in the guinness book I remember seeing a really long name of a town in wales who have a website with that name.

But limit it to 64 chars for the sake of sanity :-)

As far as subdomains: again, any segment of a FQDN (fully qualified domain name) can be upto 64 chars.

Then as you know, there are the TLDs, which the longest i know of is .museum (which will come out pretty soon).

For the username before the @ sign, it depends on the e-mail system. I think sendmail allows 256 (not sure). Qmail, being more recent, may allow more.

If you ask me: if you don't have a very large audience using this validation, then stick with 256 chars of maximum COMBINED domain name (w/ the subdomains, etc) and 128 for the stuff before the @ sign.

I would really like to see a person who has a longer (and valid) email address than that!

-sridhar

lenhewitt

Mark,

Have you considered validating the DNS entry?

$host = substr(stristr($formVars[\"email\"],\'@\'), 1)

if(!((getmxrr($host, $temp))
||checkdnsrr(gethostbyname($host),\"ANY\")))
/ There must be a Domain Name Server (DNS)
record for the domain name/
$errors[\"email\"] =
\"The e-mail address you supplied\".
\" is not a valid address\";

(Isn\'t supported under the Windows PHP build)