Use WSDL to construct your SOAP client. Even though a service endpoint URL is indicated in the WSDL, you must provide a location URL to your SOAP toolkit. This is necessary to transmit the application ID and the WSSID. In addition, you must set the cookie header containing the cookie that was returned with the WSSID when you credentialed the user in the previous step.
Not all languages that support SOAP are compatible with the Yahoo! Mail Web Service, but all languages that support JSON-RPC are.
First of all, there’s support for the non-SOAP (JSON-RPC) version in more languages, secondly, the way SOAP is used here is so exotic it’s pretty unlikely any client developer will figure out how to use it anyway.
Maybe even more absurd is a fact noted by Dare Obasanjo:
[A]lthough Yahoo! provides SOAP and RESTful JSON web services for accessing one’s mail, I still can’t get POP access to my Yahoo! mail without shelling out $20/year.
OK, I know, I know, company firewalls usually block POP and IMAP traffic. But still, shouldn’t the first protocol used for exposing a mail service actually be a mail protocol?
P.S. I’m continually amazed at the English language’s ability to “verb” nouns. “Credentialed”? Are you kidding?