Hi Christina, 

Welcome to Box Community and glad to assist! 

If your collaborator's not receiving notifications email, please check out these troubleshooting steps. 

• Check your Spam/Junk email folder. Sometimes, certain email clients do not recognize email from box.com. If you find Box messages in your Spam or Junk folder, add noreply@box.com to your email contacts, or Safe senders list. This will allow most mail clients to recognize Box emails and deliver them to your Inbox.


• 
  Firewall, Content Filter, or Email Security Policy: Check if your firewall or virus scan is blocking the email notifications. Contact your Internet Service Provider (ISP) or Corporate IT department and ask that emails from the following domains be added to the email allow list (safe sender) to ensure that Box messages are not blocked.
  
  • box.com
  
  
  • notify.box.com
  
  
  • reply.box.com
  
  
  • track.box.com
  
  


• 
  Incorrectly typed email address: Is the sender using your correct email address? Just one mistyped letter will cause an email to go to the wrong address or make it undeliverable. Ask them to double-check that they entered your address correctly.


• 
  Email on suppression list: If Box notifications ever bounce, emails are automatically added to our suppression list. If the email address(es) is correct and able to receive emails, it can be removed from our suppression list. To do so:
  
  • Log in to the Admin Console and navigate to the Notifications settings.
  
  
  • Remove the affected email address(es) using the Suppression List feature.
    
    One avoidable reason for getting on the Box suppression list is from creating a new Box account before your actual mailbox or email account is set up.
    
    
  
  


• 
  Email scanning issues: If you are experiencing scanning issues, check the HTML code of the templates for any changes and adjust your scripts.

For reference, please use this article. 

Hope it helps!