SQL & PL/SQL :: Using UTL_SMTP To Send Simple Emails

I tried using UTL_SMTP to send simple emails. My code is as follows:-

PROCEDURE prc_send
IS
- variable to hold the smtp server connection
v_smtp_connection utl_smtp.connection;
-- variable to hold the contents of the email message
v_smtp_host VARCHAR2(100) DEFAULT 'smtp.server.com';
-- variable to hold the smtp port
v_smtp_port NUMBER DEFAULT 25;
BEGIN
-- establish the connection to the smtp server
[code].........

When I execute this, It shows authentication error. Error looks like ORA-29278: SMTP transient error: 454 5.7.3 Client was not authenticated. I know my smtp server requires password authentication. But I am not aware of how to do it with UTL_SMTP.