Lookup for "550 2.6.5"
This status code indicates a successful delivery or other operation. Any details are simply notes.
Basic Status Code Details (550)
Requested action not taken: mailbox unavailable [E.g., mailbox not found, no access]
Enhanced Status Code Details (2.6.5)
Conversion Failed
A conversion was required but was unsuccessful. This may be useful as a permanent or persistent temporary notification.