Hi,
I also upgraded my osticket version from 1.10 to 1.15. At the same time, I changed my smtp server. After changing the smtp server, I got similar error as above.
After checking the smtp server log, I found that, host name is received as "localhost" in helo message. As per my knowledge, I had correctly configured the hostname in my osticket server. After doing lot of troubleshooting, I could solve it by changing the host name from "localhost" to correct hostname in include/pear/Mail/smtp.php file, in below noted line.
I do not know whether this is correct. I am not sure whether it will cause any other issue. I expect your support to do the needful in proper way. Please find details of my setup below.
Thank you.
