Neither @Tut nor myself are developers of the program. We are just end users like yourself.
I am not convinced that email invoice scan functionality would be viable for a number of reasons, the big one being the inability to scan to individual records, but there are also many other reasons why its likely to create more problems than it solves.
However, in the roadmap there is functionality coming that will enable users to scan attachments to individual records. I suspect that the procedure will be to use scanner to scan onto computer and then import into Manager. Obviously you would need a scanner and scanning software but standalone scanners are so cheap and even network scanners can be had for a low price I don’t see this as a problem.