Form mail not sending after upgrade from 5.4.2 to 5.6.1.2

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I recently upgraded a site from 5.4.x to the latest version, 5.6.2.
I just realized that forms have not been sending confirmation emails.
I've tried everything I can think of, from adding:
define('EMAIL_DEFAULT_FROM_ADDRESS', [email protected]');
define('FORM_BLOCK_SENDER_EMAIL',[email protected]');

on into testing every single possible mail PHP/SMTP function that BH gives the info for. From using a '+' and '@' on down to mail.domain.com/box123.domain.com.
No dice anywhere. Default mail logs show "Unable to send mail'. SMTP logs vary: Connection timed out, Relaying is administratively denied, Could not read from box123.bluehost.com. All depending what I had in SMTP. Contacted BH support and they said as long as I have the email created that I'm sending from it should work.

Prior to the upgrade, it used to send using my email since I was the admin/first account. That worked no problem. Not sure what happened. I find it odd that my email was working as the send email when it wasn't even on the domain, but that's just me.

Huckleberry
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Huckleberry replied on at Permalink Reply
Huckleberry
UPDATE:
Did a fresh install of c5. Imported the upgraded site's db. Same issue. Still can't mail.
Did a vanilla install of c5, added form, submitted. Same error. Can't send.
Here's the logged success and error message. Anyone else encountering this? I'm on BlueHost. Thanks in advance for the help.
**EMAILS ARE ENABLED. THIS EMAIL WAS SENT TO mail()**
Template Used: block_form_submission...

Next is error:
Mail Exception Occurred. Unable to send mail: Unable to send mail. 
#0 /home1/path/to/site/concrete/libraries/3rdparty/Zend/Mail/Transport/Abstract.php(348): Zend_Mail_Transport_Sendmail->_sendMail()
#1 /home1/path/to/site/concrete/libraries/3rdparty/Zend/Mail.php(1194): Zend_Mail_Transport_Abstract->send(Object(Zend_Mail))
#2 /home1/path/to/site/concrete/core/helpers/mail.php(349): Zend_Mail->send(NULL)
#3 /home1/path/to/site/concrete/core/controllers/blocks/form.php(454): Concrete5_Helper_Mail->sendMail()
#4 /home1/path/to/site/concrete/core/models/block.php(411): Concrete5_Controller_Block_Form->action_submit_form()
#5 /home1/path/to/site/concrete/startup/process.php(283): Concrete5_Model_Block->passThruBlock('submit_form')
#6 /home1/path/to/site/concrete/dispatcher.php(244): require('/home1/path/to/...')
#7 /home1/path/to/site/index.php(2): require('/home1/path/to/...')
#8 {main}
Template Used: block_form_submission
To: any@domain.com
From: concrete5-noreply@domain.com
Reply-To: some@body.com
Subject: Home Form Submission