When i have sending magento order mail, following exception generated at every time. how to fix it ?
2016-06-23T03:58:08+00:00 ERR (3): exception 'Zend_Mail_Transport_Exception' with message 'Unable to send mail. ' in /home/embiconi/public_html/lib/Zend/Mail/Transport /Sendmail.php:137 Stack trace:
0 /home/embiconi/public_html/lib/Zend/Mail/Transport/Abstract.php(348): Zend_Mail_Transport_Sendmail->_sendMail() 1 /home/embiconi/public_html/lib/Zend/Mail.php(1194): Zend_Mail_Transport_Abstract->send(Object(Zend_Mail)) 2 /home/embiconi/public_html/app/code/core/Mage/Core/Model/Email /Queue.php(241): Zend_Mail->send() 3 [internal function]: Mage_Core_Model_Email_Queue->send(Object(Mage_Cron_Model_Schedule)) 4 /home/embiconi/public_html/app/code/core/Mage/Cron/Model /Observer.php(326): call_user_func_array(Array, Array) 5 /home/embiconi/public_html/app/code/core/Mage/Cron/Model /Observer.php(72): Mage_Cron_Model_Observer->_processJob(Object(Mage_Cron_Model_Schedule), Object(Mage_Core_Model_Config_Element)) 6 /home/embiconi/public_html/app/code/core/Mage/Core/Model/App.php(1357): Mage_Cron_Model_Observer->dispatch(Object(Varien_Event_Observer)) 7 /home/embiconi/public_html/app/code/core/Mage/Core/Model/App.php(1336): Mage_Core_Model_App->_callObserverMethod(Object(Mage_Cron_Model_Observer), 'dispatch', Object(Varien_Event_Observer)) 8 /home/embiconi/public_html/app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('default', Array) 9 /home/embiconi/public_html/cron.php(76): Mage::dispatchEvent('default') {main}