It’s an FYI. Because the letter F begins with a vowel sound, we use the article "an".

It’s an FYI. The abbreviation FYI (For Your Information) is typically pronounced as individual letters. Because the letter F begins with a vowel sound, we use the article an.

Just as an FYI, I’m dealing with a similar issue.

Just as a FYI, I’m dealing with a similar issue.

Remember, when choosing between "a" and "an", it's the sound (not the spelling), which is important.

Is this an FYI email?

Similarly, we use "an" to say "an F", "an FBI investigation", "an FDA advisory committee", etc. since these acronyms, starting with "F", are pronounced as separate letters as well.

She became an FBI informant.