Received email from iwork@apple.com - is this an authentic address?

Looks like a scam or phishing attempt.

1. While technically the iwork@apple.com address is theoretically valid, iWorks was an old suite of office apps developed by Apple. no reason for any support team from Apple to be using an address like that.
2. "The Reminders Team" is kind of a strange name for any team of any kind to call themselves. What does that even have to do with Apple Discussions forum? Seems odd at best.
3. No, normally, neither Apple themselves, nor the Apple discussions forum staff are known to send unsolicited emails to further understand an issue. They would request it directly in the post you made here if they really needed that.
4. Also strange, they do not use your forum name, nor identify the problem they are wanting to discuss at all. If you have posted more than one post here, which is quite normal, it would be impossible to know which one they are talking about.

I would ignore the message. You can always forward it to Apple for further investigation at reportphishing@apple.com

See here for details: Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

The e-mail address that is associated with your Apple Discussions account should be private. Therefore, as long as you haven’t published it anywhere, the only way for someone to know if you posted a question about Reminders would be if they really were Apple and had your e-mail address.

There is an e-mail address for the Apple Community Hosts on the Apple Support Communities Terms of Use page that you can use to confirm all of this.

I've received these in the past although it doesn't happen very often. In my case they usually would address me somewhere by the alias I used here. As long as they aren't asking for personal information (credit card numbers, SSN, etc.) the risk is low and don't volunteer that information. If they left a valid phone number call it. Or call Apple's main number and ask to be transferred to it.