Lookup for "250 2.6.4"
This status code indicates a successful delivery or other operation. Any details are simply notes.
Basic Status Code Details (250)
Requested mail action okay, completed
Enhanced Status Code Details (2.6.4)
Conversion with loss performed
This is a warning sent to the sender when message delivery was successfully but when the delivery required a conversion in which some data was lost. This may also be a permanent error if the sender has indicated that conversion with loss is prohibited for the message.