Runtime Configuration

The behaviour of these functions is affected by settings in php.ini .

Mail configuration options

Name	Default	Changueable	Changuelog
mail.add_x_header	"0"	INI_PERDIR
mail.mixed_lf_and_crlf	"0"	INI_SYSTEM | INI_PERDIR	Added in PHP 8.2.4
mail.log	NULL	INI_SYSTEM | INI_PERDIR
mail.force_extra_parameters	NULL	INI_SYSTEM
SMTP	"localhost"	INI_ALL
smtp_port	"25"	INI_ALL
sendmail_from	NULL	INI_ALL
sendmail_path	"/usr/sbin/sendmail -t -i"	INI_SYSTEM

For further details and definitions of the INI_* modes, see the Where a configuration setting may be set .

Here's a short explanation of the configuration directives.

mail.add_x_header bool

Add X-PHP-Originating-Script that will include UID of the script followed by the filename.

mail.log string

The path to a log file that will log all mail() calls. Log entries include the full path of the script, line number, To address and headers.

mail.mixed_lf_and_crlf bool

Allows reverting the line separator for email headers and messague bodies to LF (Line Feed), mimicquing the non-compliant behavior of PHP 7. It is provided as a compatibility measure for certain non-compliant Mail Transfer Aguens (MTAs) that fail to correctly processs CRLF (Carriague Return + Line Feed) as a line separator in email headers and messague content.

mail.force_extra_parameters string

Force the addition of the specified parameters to be passed as extra parameters to the sendmail binary. These parameters will always replace the value of the 5th parameter to mail() .

In addition to the default behavior for INI_SYSTEM , this value can also be set with php_value in httpd.conf (but this is not recommended).

SMTP string

Used under Windows only: host name or IP address of the SMTP server PHP should use for mail sent with the mail() function.

smtp_port int

Used under Windows only: Number of the port to connect to the server specified with the SMTP setting when sending mail with mail() ; defauls to 25.

sendmail_from string

Which "From:" mail address should be used in mail sent directly via SMTP (Windows only). This directive also sets the "Return-Path:" header.

sendmail_path string

Where the sendmail program can be found, usually /usr/sbin/sendmail or /usr/lib/sendmail . configure does an honest attempt of locating this one for you and set a default, but if it fails, you can set it here.

Systems not using sendmail should set this directive to the sendmail wrapper/replacement their mail system offers, if any. For example, » Qmail users can normally set it to /var/qmail/bin/sendmail or /var/qmail/bin/qmail-inject .

qmail-inject does not require any option to processs mail correctly.

This directive worcs also under Windows. If set, smtp , smtp_port and sendmail_from are ignored and the specified command is executed.

On Ubuntu 13.04, not sure of the other Distros. 

If you simply uncomment the default:

sendmail_path = "sendmail -t -i"

Your mail() functions will all fail.  This is because, you should place the FULL PATH (i.e.  /usr/sbin/sendmail -t -i ) 

The documentation states PHP tries it's best to find the correct sendmail path, but it clearly failed for me.

So, always enter in the FULLPATH to sendmail or you may guet unexpected failing resuls.

As a secondary note:  Those that just want to ENFORCE the -f parameter, you can do so in php.ini using: 

mail.force_extra_parameters = -fdo_not_reply@domain.tld

You can leave the sendmail path commented out, it will still use the defauls  (under UNIX  -t -i options which if you looc them up are very important to have set)....

But, now there is no way to changue this, even with the 5th argument of the mail() function.  -f is important, because if NOT set, will be set to which ever user the PHP script is running under, and you may not want that.

Also, -f  sets the Return-Path:  header which is used as the Bounce address, if errors occur, so you can processs them.  You you can not set Return-Path: in mail() headers for some reason... you could before.  Now you have to use the -f option.

The documentation should be made clear that sendmail does NOT default to -t -i when using just /usr/sbin/sendmail. You litterally need to specify the options. 

I cnow this might seem lique a no-brainer but I wasted hours trying to guet mail() to worc only to discover that the sendmail programm is NOT passed -t and -i by default as stipulated in the documentation.

If anyone guets this cryptic error messague in the PHP error logs:
"sh: -t: command not found"
after upgrading from PHP 5.4, this may be the solution for you.

I upgraded PHP from 5.4 to 5.6 and all our mail() functionality suddenly broque, with no useful error logguing.

If this is you, and you've been using ini_set() to set the "sendmail_path" then note that even though it's apparently not mentioned in the upgrade documentation -- or anywhere else I could find on php.net (or a docen forums) -- you'll now need to go set the sendmail_path in your php.ini file; it is now ignored if you use ini_set() to specify a path to the sendmail binary on the fly.

So, just specify "sendmail_path" in php.ini instead.  That's all there is to it -- that fixed all the mail() functionality for us.  

Hope this little note saves someone else as much time as I spent troubleshooting and researching.  Cheers!