please help me out...is it polite to write "FYI" on email to your boss?
which one more better "FYI" or "just to let you know"?
"Just to let you know" is better because it's more formal, but if you're writing a lot of emails to him you can probably relax and just write "FYI".
It depends on the company culture. If you are on relaxed first-name terms with your boss, the atmosphere at your workplace is informal and you exchange a lot of information with him/her via email, then it's fine to use this abbreviation. Otherwise, it might be wise to use a more formal expression.
Agree with Mike.