I have setup MantisBT with PostgreSQL database. Everything working fine except Email notification.
My SMTP settings are as below.
The password starts with '#' character. Is that a problem. Another application is already working with this SMTP configuration.

SMTP log as below:
2018-03-08 09:27 IST MAIL email_api.php:1396 email_send() ERROR: Message could not be sent - SMTP Error: Could not authenticate.

$g_enable_email_notification = ON;
$g_phpMailer_method = PHPMAILER_METHOD_SMTP;

$g_smtp_host = '...';
$g_smtp_port = 25;
$g_smtp_connection_mode = '';
$g_smtp_username = 'domain\user';
$g_smtp_password = '****'; #password starts with '#' character

$g_administrator_email = 'email@gmail.com';
$g_webmaster_email = 'email@gmail.com';
$g_from_email = 'email@gmail.com';
$g_return_path_email = 'email@gmail.com';
$g_from_name = 'Issue tracker';
$g_email_receive_own = OFF;
$g_allow_file_upload = ON;
$g_validate_email = ON;
$g_allow_blank_email = ON;
$g_email_send_using_cronjob = ON;