Sending emails to Multiple Recipients using UTL_SMTP

I have a stored procedure created using the Oracle Note ID 744605.1 to send emails to Multiple Recipients using UTL_SMTP but its not working.
When did a test, it says Your e-mail was successfully sent but I am not getting any emails.
Sample Syntax,

EXEC send_mail('sender@domain.com', 'recipient1@domain.com, recipient2@domain.com, recipient3@domain.com', 'Subject of TEST EMAIL USING UTL_SMTP', 'Body of TEST EMAIL USING UTL_SMTP');
I also tried with one email recipient but still no email was generated. Not sure what was causing the problem. Any one using UTL_SMTP to send emails to multiple recipients, please advise.