Error Plesk External mail

Delivery to the following recipient failed permanently:

     [email protected]

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain sleepbcn.com bymail.sleepbcn.com. [92.222.231.206].

The error that the other server returned was:
554 5.7.1 <[email protected]>: Relay access denied


----- Original message -----

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Date: Wed, 28 Oct 2015 21:49:43 +0200
Message-ID: <CAKpWe5Wj05C1RvoM1bBKuEax4N0H9j=YOsqiLa4gw=ah7Jq3bw@mail.gmail.com>
Subject: Prueba de correo
From: Alexandru Trandafir Catalin <[email protected]>
To: [email protected]
Content-Type: multipart/alternative; boundary=047d7bd6b5e4ec9b8305232f7e8b

Prueba de correo