What do not tell me, I just discovered that I can not send more than 500 mails per day from the web interface of google mail (gmail)
in other words there is a max. number of sent messages per day if you are using google mail (gmail) web interface and they will stop your account from sending any more mails.
Thankx to my blog, I just knew that when I was sending my blog announcement
another useful link regarding the same topic is here
Google Link regarding this mail send limit is here
Have a Nice day