Sender domain registered in Email Security Cloud is unable to send an email to external 3rd party recipient and is encountering error 550 Administrative prohibition - envelope blocked - https://community.mimecast.com/docs/DOC-1369#550 [RHtMGohWOQGj8zZhoUdmKA.uk207]"
Environment
Email Security.cloud
Resolution
Recipient is using Mimecast as their Email Service Provider and is blocking emails from the sender.
Recipient should be contacted in such cases to check if there are any blocked policies defined for the sender on their end and then exclude the sender so that emails can be allowed.