Why is Mail Drop not working for Photos on my iPhone

Why is Mail Drop not working when used with the Apple Photos app on my iPhone. (It's an iPhone Pro Max running the latest OS.)

Scenario: I select a dozen photos in the Photos app and specify to 'share' using the email icon. Photos responds that what I've selected is too large (it is) and presents the Mail Drop option. I select that. The photos never show up to the recipient - nor do they show up in iCloud.

I see that I need to be on (at least) Yosemite for it to work on my computer (& I'm still on High Sierra). But shouldn't I see the sent email with the photos show up in iCloud??

Thanks.