i post the next message to my zimbra server

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
<soap:Header>
<context xmlns="http://serverzimbra/service/soap"></context>
</soap:Header>
<soap:Body>
<AuthRequest xmlns="urn:zimbraAdmin">
<account by="name">mail</account>
<password>11111</password>
</AuthRequest>
</soap:Body>
</soap:Envelope>

but i only get a 500 error what is wrong with my message??

Thanks for your help