after Magento upgrade from v1.9.1.0 to v1.9.2.0 mails stopped sending. In system.log I see an error HRADERS ALREDY SENT. However, this message appear when I press Add to cart button, but users' checkout process goes smoothly. Moreover, I see successful orders in the dashboard where it is said that customer is notified and status order - pending. Thus, I am not sure whether this issue causes problem with email.
In addition, I have a list of files in system.log that are loaded and probably have white space or BOM and I checked them but found nothing. The list contains 334 files, so it is possible that I miss something. Is there a way to find a file that causes Headers error ?
Also, I checked if I can send email just using mail() from "simple" php - it works.
How to start solving problem with emails. I read that I should select crone.php in cPanel, and I did it. How to know whether emails are not being formed or could not be sent?