Lookup for "535 2.7.5"
This status code indicates a successful delivery or other operation. Any details are simply notes.
Basic Status Code Details (535)
Authentication failed due to invalid or insufficient authentication credentials
Enhanced Status Code Details (2.7.5)
Cryptographic failure
A transport system otherwise authorized to validate or decrypt a message in transport was unable to do so because necessary information such as key was not available or such information was invalid.