Application Express :: 4.2 - Oracle Apex_Mail Send

I am using oracle apex 4.2 version.i am trying to send mail using APEX_MAIL.send.My process like

begin
APEX_MAIL.send(
p_to       => 'xxx@xxx.com',
p_from     => 'xxx@xxx.com',
p_body     => l_body,
p_subj     => 'APEX_MAIL Package - Plain Text message');
end;

When i check mail queue from administrator part HomeManage > InstanceMail > Queue

It show no error and after the send all mail still i am not getting the mail..i also check my email setting in administrator part.