Needs checking: real brands rarely do it, scammers imitate it
"Your video uses my music without permission": the fake claim by e-mail
An artist or rights holder writing to you about music "used without permission", a complaint "about to be filed", then a file of evidence to open: a scam aimed at your account, not at your rights.
What it looks like
As an independent artist, it seems this music is used on your channel without my permission. I would rather wait before filing a complaint. However, my distribution platform is about to issue a formal claim.
Why it is a sign
A real rights claim goes through YouTube, and you see it in YouTube Studio, with the video's title and the track at stake. This one comes by e-mail, names neither video nor track, starts kindly, then sends a "file of evidence" or a "codec" to download: that is what steals the account. These campaigns go out in bulk to the public addresses of channels.
What a real brand does
A serious rights holder files its claim in YouTube's tool, and you find it in Studio. It has no need for you to open a file.
What to do
Look in YouTube Studio for a claim on the video. If there is none, do not answer and open nothing. If there is one, that is where it gets settled, not by e-mail.