In Google Talk, how to send a message to person that is not in my friend list?
I work on an application that notify customers of a bank about change of their accounts. When I send a message to a person not in my list, no error is created, but the message isn't delivered to the recipient.
Because of design issues it is not suitable to send an invitation to customers and store information about their responses to it.
You can message a user directly using XMPP without an active presence subscription (the requirement for an item to appear in your roster), but most clients (Google Talk clients included AFAIK) will discard the message upon reception, if the from header does not match a bare JID in their roster.