Lookup for "251 2.7.0"
This status code indicates a successful delivery or other operation. Any details are simply notes.
Basic Status Code Details (251)
User not local; will forward to
Enhanced Status Code Details (2.7.0)
Other or undefined security status
Something related to security caused the message to be returned, and the problem cannot be well expressed with any of the other provided detail codes. This status code may also be used when the condition cannot be further described because of security policies in force.