Could anyone tells me what this means please?
Mail Delivery Subsystem to me
show details 17 Mar
Delivery to the following recipient failed permanently:
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 #5.1.0 Address rejected firstname.lastname@example.org (state 14).