sending failed: relaying disallowed

Sending failed:
The message content was not acepted.
The server responded: "Relaying disallowed"
The message will stay in the "outbox" folder until you either fix the problem
(e.g. a broken address) or remove the message from the "outbox" folder.
The following transport was used:
césar tejui

ANY SUGGESTIONS WILL BE APPRECITAED.
BEST REGARDS,

CÉSAR