Is the following an informal or formal communication channel?

memo addressing new dress code policy

a. formal
b. informal

There is debate as to wheter memos are informal or formal. This is because people have different idea of the contents of a memo. Consider a memo about a disciplinary action, which is a more formal memo. While an informal memo might be about planning for a big party. In this, since the memo is about a new dress code policy, I would say it would be considered formal (A).

c. barbarians with unexpected intelligence