Queued component keeps retrying

Got a problem using a VB queued component that sends emails via an SMTP server.

It creates an instance of the CDO.Message object , loops through a record set of Recipients, puts the message together, then sends the email. What I'm finding is that after the recordset returns a certain number of Recipients (around 130), instead of sending 130 emails, it'll send, say 500.

I think that for some reason message queue is thinking that it hasn't successfully "sent" the message, so it retrys - creates a new instance of the component, and off it goes. The larger the number of recipients it loops through, the greater the extra numbers of emails as it works it's way throught the retry queue.

If I remove the component from Message Queue, it sends the correct number of emails every time. I've also tried pointing it at our Exchange server and it works fine every time. However using a SMTP server it gets stuck in this retry thing.

I originally wrote the component in C# using the SMTPMail object. In the process of trying to narrow down what's happening I changed to to VB6 using CDOSYS just in case it was something to do with the .net interop. Message Queue would definately seem to be the culprit.

Has anyone ever hit anything like this before??