ORA-20000: Unable to send mail: ORA-29279: SMTP permanent error: 500 5.3.3 Unrecognized command ORA-

Dear friends,

This is my code to send email outside the domain via Database (10g)10.2.0.5 version on windows 2008 64bit operating system

DECLARE

   v_From       VARCHAR2(80) :=  'zain@cdscomp.com';--'zain@cdscomp.com';

   v_Recipient  VARCHAR2(80) := 'arhaan6cgmail.com';--'zain@cdscomp.com';

   v_Subject    VARCHAR2(80) := 'test subject';

   v_Mail_Host  VARCHAR2(30) := 'x.xx.x.x';--'cds-mail.CDSCOMP';

   v_Mail_Conn  utl_smtp.Connection;

crlf         VARCHAR2(2)  := chr(13)||chr(10);

message VARCHAR2(10000) := 'test send mail '; 

BEGIN

  v_Mail_Conn := utl_smtp.Open_Connection(v_Mail_Host,25);

    utl_smtp.command( v_Mail_Conn,v_Mail_Host);       --- mail server name

    utl_smtp.command( v_Mail_Conn