reading/writing things that lead to anger

I have an email that I have to reply to, ideally by tomorrow.

When I first read the email yesterday afternoon I couldn't make it through to the end without becoming intensely angry. The second time, just glancing at it brought back the same anger. Today I've been afraid to open it because I don't want to feel that way if I don't have to.

But I do have to respond and there's a bunch of questions in the email that I need to answer. The person didn't say anything aggressive in the email, but it's the type of questions they've asked that are extremely frustrating and the fact is that for some of the questions (it's a long email) they're not asking the right person and I don't think they'll understand the answer even if they did.

I'm literally afraid to open this email which is ridiculous but I don't know how to do it.