I config my Q2A admin email is email@example.com It worked well until yesterday (I received notification email when a question was posted). I asked hosting service provider, here is the answer but I dont understand the solution. So just post here if anybody has the same problem can explain more for me:
-- From hosting provider:
I checked the mail logs, Google seems to have blocked mail from your address due to the 'unusual amount' that it is sending. Are you sending more mail than usual? Do you have the option to use the "-f" switch in your sendmail statement?
What Corey was describing is a way for you to force sendmail to send mail from a specific address, rather than an address general to the server.
Applications sending mail directly through the sendmail command usually provide some method for you to alter arguments being passed to sendmail. What opensource system are you using? Using this may help ensure deliverability for your email.