Ensuring email delivery on Workplace

Email Domains
Emails that are sent by Workplace will originate from the domain fbworkmail.com.
Your email administrator must add fbworkmail.com as a safe sender to your email host, otherwise people in your organization won't be able to receive claim account emails and won't be able to join your Workplace community.
Email Servers
Your email administrator must whitelist these email origin servers' IP addresses to ensure that your organization doesn't reject Workplace emails.
66.220.144.128/25 (66.220.144.128 - 66.220.144.254)
66.220.155.128/25 (66.220.155.128 - 66.220.155.254)
69.171.232.128/25 (69.171.232.128 - 69.171.232.254)
69.63.178.128/25 (69.63.178.128 - 69.63.178.254)
69.63.184.0/25 (69.63.184.0 - 69.63.184.126)
Verifying Email Origin
To prove that emails coming from fbworkmail.com actually originate from Facebook, Workplace uses the industry standard technology DomainKeys Identified Mail (DKIM).
Your email administrator should configure your mail host to verify the DKIM record of all Workplace emails to ensure that you don't accept spoofed emails.