How can you disable Magento's default newsletter confirmation email?
There are a few options that are explained here:
Unfortunately most of them are fairly technical and not very simple solutions. We are hoping to add native support for this at some point in the MageMail connector. One of the reasons we haven't done this to date is that it would likely require a class rewrite, which is one of the techniques that can tend to cause conflicts with other extensions, which we try to keep to an absolute minimum.