I can't accept invitation to subscribe to a shared photo album

I'm on a mac running OS X 10.10.5. I use gmail for my mail. My version of iphoto is 9.6.1. I received an invitation to subscribe to a shared photo album. When I click on 'subscribe', I get the message (where I've substituted XXX for the name of the album):

Shared albums are not available for this device.

To subscribe to XXX shared album on

your iPhone, iPad, iPod touch, or Mac, open your invitation in the Mail

app, and click the Subscribe button in the message.

To subscribe you need to be signed in to iCloud on:

• An iPhone, iPad, or iPod touch with iOS 6 or later, or
• A Mac with macOS 10.8.2 or later and iPhoto 9.4 or Aperture 3.4 or later

So it looks like Apple is requiring me to use its own Mail app in order to subscribe?? Is there any way around this? I don't right off know how to get my gmail into Mail without losing it on gmail and frankly I don't want to have to figure this out just to share an album -- is there any way to accept the invitation without doing it in Apple mail??

Thank you.