XF 1.5 Zend_Mail_Transport_Exception Error

[Yung]

I got this error after upgrading to 1.5.14. It seems that xenforo can't send any email to user. Any idea how to fix this?
The error below is from an execution to send email to user when new conversation is started

Error Info
Zend_Mail_Transport_Exception: Email to abs@gmail.com failed: Unable to send mail. mail() has been disabled for security reasons - library/Zend/Mail/Transport/Sendmail.php:137
Generated By: Unknown Account, 1 minute ago
Stack Trace
#0 /home/abc/public_html/forum/library/Zend/Mail/Transport/Abstract.php(348): Zend_Mail_Transport_Sendmail->_sendMail()
#1 /home/abc/public_html/forum/library/Zend/Mail.php(1194): Zend_Mail_Transport_Abstract->send(Object(Zend_Mail))
#2 /home/abc/public_html/forum/library/XenForo/Model/MailQueue.php(79): Zend_Mail->send(Object(Zend_Mail_Transport_Sendmail))
#3 /home/abc/public_html/forum/library/XenForo/Deferred/MailQueue.php(10): XenForo_Model_MailQueue->runMailQueue(7.9999980926514)
#4 /home/abc/public_html/forum/library/XenForo/Model/Deferred.php(295): XenForo_Deferred_MailQueue->execute(Array, Array, 7.9999980926514, '')
#5 /home/abc/public_html/forum/library/XenForo/Model/Deferred.php(429): XenForo_Model_Deferred->runDeferred(Array, 7.9999980926514, '', false)
#6 /home/abc/public_html/forum/library/XenForo/Model/Deferred.php(374): XenForo_Model_Deferred->_runInternal(Array, NULL, '', false)
#7 /home/abc/public_html/forum/deferred.php(23): XenForo_Model_Deferred->run(false)
#8 {main}
Request State
array(3) {
["url"] => string(46) "http://www.domain.com/forum/deferred.php"
["_GET"] => array(0) {
}
["_POST"] => array(4) {
["_xfRequestUri"] => string(32) "/forum/conversations/add?to=Abc"
["_xfNoRedirect"] => string(1) "1"
["_xfToken"] => string(8) "********"
["_xfResponseType"] => string(4) "json"
}
}

 

[Paul B]

The mail function has been disabled on the server.

mail() has been disabled for security reasons

Your sysadmin or host will need to resolve that.