How do i know if he needs a 2 factor authentification?

Hi Ulrike, 

Welcome to Box Community and glad to help! 

You can advise the user to contact our team directly so we could get a closer look. Meanwhile, please have him to run these troubleshooting steps for Email Notifications. 

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. Open a case with the support team to check the affected email address(es). 

Hope it helps!