Invalid sendmail "from" in php_fpm_pool.conf.master
Actual code: php_admin_value[sendmail_path] = "/usr/sbin/sendmail -t -i -fwebmaster@<tmpl_var name='domain'>"
If should be: php_admin_value[sendmail_path] = "/usr/sbin/sendmail -t -i -f webmaster@<tmpl_var name='domain'>"
Please note the missing space between the -f and webmaster@