XF 1.5 Server Error Logs

hi 2 day when i log on my panel admin see this error :
Server Error Log
Error Info
Zend_Mail_Transport_Exception: Email to castlelas@gmail.com failed: Unable to send mail. - library/Zend/Mail/Transport/Sendmail.php:137
Generated By: Unknown Account, 51 minutes ago
Stack Trace
#0 /home/kikdirty/public_html/library/Zend/Mail/Transport/Abstract.php(348): Zend_Mail_Transport_Sendmail->_sendMail()
#1 /home/kikdirty/public_html/library/Zend/Mail.php(1194): Zend_Mail_Transport_Abstract->send(Object(Zend_Mail))
#2 /home/kikdirty/public_html/library/XenForo/Model/MailQueue.php(79): Zend_Mail->send(Object(Zend_Mail_Transport_Sendmail))
#3 /home/kikdirty/public_html/library/XenForo/Deferred/MailQueue.php(10): XenForo_Model_MailQueue->runMailQueue(7.9897100925446)
#4 /home/kikdirty/public_html/library/XenForo/Model/Deferred.php(295): XenForo_Deferred_MailQueue->execute(Array, Array, 7.9897100925446, '')
#5 /home/kikdirty/public_html/library/XenForo/Model/Deferred.php(429): XenForo_Model_Deferred->runDeferred(Array, 7.9897100925446, '', false)
#6 /home/kikdirty/public_html/library/XenForo/Model/Deferred.php(374): XenForo_Model_Deferred->_runInternal(Array, NULL, '', false)
#7 /home/kikdirty/public_html/deferred.php(23): XenForo_Model_Deferred->run(false)
#8 {main}
Request State
array(3) {
["url"] => string(33) "https://kikdirty.com/deferred.php"
["_GET"] => array(0) {
["_POST"] => array(4) {
["_xfRequestUri"] => string(38) "/forums/kik-usernames.40/create-thread"
["_xfNoRedirect"] => string(1) "1"
["_xfToken"] => string(8) "********"
["_xfResponseType"] => string(4) "json"

many other email but same error !! what happened?


XenForo developer
Staff member
If you haven't resolved this, you'd either need to contact your host or change XenForo's email settings to use an external SMTP server.
I was already using an external e-mail, if I were to use the email exenforo what would be?specifically which settings should I change? as in the design of the links that you have previously shown?


XenForo developer
Staff member
That specific error only occurs if you're using the default PHP mail option, not an external SMTP server. If you don't remember changing the settings in XenForo, it's worth double checking the email setting specifically to confirm it's what you expect.