Settings to ensure guest users receive notifications

[Jenonthetrain]

Hello, we have colleagues at an outside company and have set them up as Guest Users to access shared content via Teams. When we create a post and tag the guest users, sometimes they receive notifications in Outlook but more often they don't, so we've started alerting them via email. Which defeats the purpose of using a Teams post. Their Teams is set to relay notifications every hour, but it's not happening. 
Are there other settings we can pursue to make sure the Guest Users receive their notifications?

[#2]

Users are in control of their notification settings, including email notifications. There's no "admin override" for that afaik.

[#3]

This is literally the third year of a pandemic, millions of agencies worldwide are working form home, and MS Teams hasn't figured out how to send notifications to guests.

I have spent at least one hour trying to figure out how to help my clients with their notifications and all i see is people complaining and MS Teams not responding or actually doing something. So disappointing, especially if we consider how quickly small agencies have evolved lately, and big companies don't even help users with notifications.  @Jenonthetrain 

[#4]

@TheodoraDeltona I had the same issue and determined that my guest access used Custom settings for notifications. i enabled "All Activity" and now I see the new posts. Hope this helps.