An address that answers on one date and rejects on another has changed state. The rejection message is generated by the receiving organization’s own server, which makes it evidence the sender could not fabricate.
What the codes distinguish
550 5.1.10 means the address does not resolve to a mailbox. 550 5.4.1 means the system refuses to accept the message. An account producing one and then the other has changed twice.
The limit that must be respected
Transport records do not identify the administrator, the policy, or the lifecycle event responsible, and they do not prove destruction of historical content. Claiming otherwise is overreach.
Why the limit is the strongest position
Every record that could explain it benignly sits inside the organization’s own systems and exports in under an hour: unified audit log, directory lifecycle events, mailbox state, retention policy, litigation-hold status, eDiscovery preservation. An organization with an innocent explanation produces them. See the documented example.