i received this enail from yahoo and wondered if it was a scam: On an iPhone or iPad, upgrade your operating system to iOS 9.3 or later. Learn how: https://support.apple.com/en-us/HT204204

I suppose you're using Yahoo Mail app for iOS instead of accessing your Yahoo mail with iOS built-in Mail app. If that's correct, Yahoo mail app does require iOS 9.3 or later:

https://itunes.apple.com/us/app/yahoo-mail-keeps-you-organized!/id577586159?mt=8

Compatibility: Requires iOS 9.3 or later.

It is not a scam. Google did something similar last year with mail authentication on most non-gmail clients (on both Android and iOS), where they stated that the clients were "not secure enough" and mail just stopped. You had to go to Google and change a setting there to "allow less secure apps". Yahoo had done something similar (not sure why you are getting this now as I thought it was a couple months ago) but the latest few versions of Android and iOS have updated mail clients I do believe.

Hello,

Here's articles about how to identify scam emails:

Phishing & Other Suspicious Emails

Identifying legitimate emails from the iTunes Store - Apple Support

Well, according to the App Store description Yahoo Mail does need at least 9.3 to run. what version of iOS are you running?