Hi,
My moodle site does not send e-mail authentication/confirmation when a new user try to register at the site (see first screen shot). I checked SMTP configuration and also tried different types of SMTPs like yahoo and gmail but it did not work. Then I checked PHP info and it came up with the result in the second screen shot and as it is seen the line, "sendmail_from" has not got any value (see second screen shot). I have read the instructions under the following link: https://docs.moodle.org/27/en/Email_settings#SMTP_hosts