You don't

Generally speaking you would not want to do that.  I'm not sure if sage will allow it as it goes against the standard workflow but there me be a way I don't know about.  

So, I do not process those invoices until the receipts are marked in the system? Once the receipts are marked, then i process the invoice against the receipts?

It's not allowed

Correct

thank you. And how do i access these conversations or mail this conversations?

Do a screenshot

Screenshot or copy paste.  Many different ways.