There have been no changes since Beta 1, so please find the release notes for v4.4.0 below:
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This version adds a single major new feature; the ability to limit the maximum amount of emails your forum sends in an hour.
To be clear, this affects all email across the whole of your XenForo installation, so long as all 3rd party add-ons use XF's own email feature.
This means if you are running your site on a shared host, or your web host is limiting the amount of email sent, you can now effectively control this within XF.