I was once a customer of a certain developer who sold a SaaS bookkeeping software which allowed sending deal documents (invoice, receipt, etc) to a customer, from the software's very own email server, and any content sent was always digitally signed.
I know that in the context of emails, at least four "aspects" can be digitally signed:
- The email server itself
- The timestamp of sending
- The sending source (email address I would presume)
- The content of an email sent (including attached files)
My questions
- In the context of emails, what can be digitally signed (did I describe the aspects accurately and/or missed a certain aspect)?
- What should be digitally signed in the sub context of deal documents (I know that some bookkeeping software don't allow digitally signing anything and I want to know why some do and some don't)