TOPIC: Formal vs Informal communication

Since email is considered to be informal and a report is considered to be formal, if I send a formal report via email (attachment) what type of communication is this?

It would be formal because your communication is contained w/in the report. In this case, email is just the delivery method.

A report is a formal document, but think of an email as the equivalent of an informal note. So your example is very similar to handing someone your report with a yellow sticky note stuck on top.