Hello,
sorry to say that, but I do not really think there is a bug in the VM Invoice as regards this issue. So far, you are the only one having the problem. Most likely, the problem must be connected with your settings, Joomla or server environment, as VM Invoice fully relies on Joomla mailing engine.
Please, post a screenshot of Mailing settings from VM Invoice & Joomla Global Configuration. It might tell more.
Neither you have answered my earlier question, if other Joomla emails are sent normally. (e.g. new registration notification mail)
Also please state your current Joomla & VM Invoice versions.
If you would be interested in a fast solution, we can also offer you a paid support and check & fix this directly at your site. I believe we will find the reason of this. (
www.artio.net/e-shop/support-services/joomla-related-support-1h)