Why is the PHP mail() function not working on the server?

Question

PHP

The simplest script.

// Send email
  if (mail($mail_to, $subject, "", $header)) {
    echo "Sent";
  } else {
    echo "Error";
  }

Gives an error all the time. It seems that the server was configured normally, all packages were installed, the paths were checked, but it does not work.
Pretty much the same server works fine with mail().
Check what? What to pay attention to? What to update?

Answer 1

Check if the mail function works at all on the server:
Check if the mail service is installed: sendmail, postfix or another.
Check if the mail service is running.
For sendmail/postfix, check the settings in php.ini:

; For Unix only.  You may supply arguments as well (default: "sendmail -t -i").
; http://php.net/sendmail-path
sendmail_path = "/usr/sbin/sendmail -t -i"

Check in php.ini if ​​the mail function is included in the list of prohibited functions:
disable_functions

Answer 2

Check if the feature is enabled.

Answer 3

is there a local SMTP server?
if in *NIX you can check from the console

echo “Test Mail” | mail -s “Hello world” [email protected]

Answer 4

mostly disabled in php.ini via disable_functions for security purposes