We have a VPS running litespeed with four website frontends on CE 1.9.2.
It is experiencing really inconsistent new order email problems. Sometimes the email goes. Sometimes it doesn't - that's close to 50/50, we then have outliers where the order email sends two or three times.
Most times when the email doesn't send automatically, I can manually queue another email and it will send on schedule, although sometimes I have to do that twice to get a success.
Looking at the exception log on the failures we are getting a fairly generic looking exception:
ERR (3):
exception 'Zend_Mail_Transport_Exception' with message 'Unable to send mail. ' in /home/magento/public_html/lib/Zend/Mail/Transport/Sendmail.php:137
Stack trace:
#0 /home/magento/public_html/lib/Zend/Mail/Transport/Abstract.php(348): Zend_Mail_Transport_Sendmail->_sendMail()
#1 /home/magento/public_html/lib/Zend/Mail.php(1194): Zend_Mail_Transport_Abstract->send(Object(Zend_Mail))
#2 /home/magento/public_html/app/code/core/Mage/Core/Model/Email/Queue.php(239): Zend_Mail->send()
#3 [internal function]: Mage_Core_Model_Email_Queue->send(Object(Mage_Cron_Model_Schedule))
#4 /home/magento/public_html/app/code/core/Mage/Cron/Model/Observer.php(326): call_user_func_array(Array, Array)
#5 /home/magento/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/magento/public_html/app/code/core/Mage/Core/Model/App.php(1357): Mage_Cron_Model_Observer->dispatch(Object(Varien_Event_Observer))
#7 /home/magento/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/magento/public_html/app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('default', Array)
#9 /home/magento/public_html/cron.php(77): Mage::dispatchEvent('default')
#10 {main}
Please help, we have run out of ideas.