employees unable to send emails

[Pegbradbury]

Several of our employees are unable to send emails.  They get an error stating that their message could not be sent because they weren't recognized as a valid sender.  Why is this an issue and how did it become one?  How do I fix without issuing new email addresses

[#2]

Follow the instructions here: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/removing-user-from-restr...