I get this result:
Salesforce.com Lead Capture Interface
Reason: Your Lead could not be processed. null
Lead Capture Page: Not available.
Record Information:
debug = 1
encoding = UTF-8
last_name = Confetti
oid = <redacted>
retURL = http://www.yahoo.com
status = Open
submit = Submit
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at the top right of any page within salesforce.com
I have no required custom fields or validation rules. Pretty sure the oid is correct (same as the web2lead form generator spat out). I get the same result when I leave out the status field. When I leave off the debug, the page silently redirects to the url passed.
I can manually add a new lead with just the last name of "Confetti".
This was scraped from behind a NAT, but I get the same result when posted from a public IP address - even a Visualpage form in the same salesforce app.
Do they do ip filtering, maybe?
My form (without the status):
<!DOCTYPE html>
<html>
<head>
<title>Test!</title>
<META HTTP-EQUIV="Content-type" CONTENT="text/html; charset=UTF-8">
</head>
<body>
<form action="https://www.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8" method="POST">
<input type=hidden name="oid" value="XXXXXXXXXXXXX">
<input type=hidden name="retURL" value="http://www.yahoo.com">
<input type="hidden" name="debug" value=1>
<label for="last_name">Last Name</label><input id="last_name" maxlength="80" name="last_name" size="20" type="text" /><br>
<input type="submit" name="submit">
</form>
</body>
</html>