The sender was refused critical
The receiver refused our envelope address before the recipient was mentioned.
In detail
One of the two states that speak purely about the sender. A refusal here means the envelope address, its domain or its SPF record was judged unacceptable — the recipient has not been named yet, so nothing about the address list is implied. In practice this is where a reputation problem announces itself most clearly, and where an SPF misconfiguration shows up as a wall of refusals across every domain at once.