Mail() function not working correctly in PHP 8.x

[hansherlighed]

Description

The following code:

<?php
mail("someone@example.com", "This is the subject", "This is the body");
?>

Resulted in this output of the DATA part of the communication from tcpdump on the receiving SMTP server when building container "FROM php:8.0.14-fpm-alpine" or "FROM php:fpm-alpine":

Received: by f3de6efeb3a0 (sSMTP sendmail emulation); Sat, 12 Feb 2022 06:28:10 +0100\r\n
From: "Linux User" <www-data@f3de6efeb3a0>\r\n
Date: Sat, 12 Feb 2022 06:28:10 +0100\r\n
To: redacted@example.com\r
\r\n
Subject: This is the subject\r
\r\n
\r
\r\n
This is the Body\r
\r\n
\r\n

And this is the resulting mail headers of the mail on the receiving SMTP server:

Return-Path: <www-data@f3de6efeb3a0>
X-Envelope-To: redacted@example.com
Message-ID: <3966183578-2392@mail.example.com>
Received: from localhost ([127.0.0.1])
	by mail.example.com with SMTP
	for redacted@example.com;
	Sat, 12 Feb 2022 06:28:10 +0100
Received: by f3de6efeb3a0 (sSMTP sendmail emulation); Sat, 12 Feb 2022 06:28:10 +0100
From: "Linux User" <www-data@f3de6efeb3a0>
Date: Sat, 12 Feb 2022 06:28:10 +0100
To: redacted@example.com

This is the output using the exact same environment, just that the container is build using "FROM php:7.4-fpm-alpine":

Received: by ae23725475da (sSMTP sendmail emulation); Sat, 12 Feb 2022 06:27:33 +0100\r\n
From: "Linux User" <www-data@ae23725475da>\r\n
Date: Sat, 12 Feb 2022 06:27:33 +0100\r\n
To: redacted@example.com\r\n
Subject: This is the subject\r\n
\r\n
This is the Body\r\n

And this is the resulting mail headers of the mail on the receiving SMTP server:

Return-Path: <www-data@ae23725475da>
X-Envelope-To: redacted@example.com
Message-ID: <3966147578-2389@mail.example.com>
Received: from localhost ([127.0.0.1])
	by mail.example.com with SMTP
	for redacted@example.com;
	Sat, 12 Feb 2022 06:27:33 +0100
Received: by ae23725475da (sSMTP sendmail emulation); Sat, 12 Feb 2022 06:27:33 +0100
From: "Linux User" <www-data@ae23725475da>
Date: Sat, 12 Feb 2022 06:27:33 +0100
To: redacted@example.com
Subject: This is the subject

The result is that when using PHP 8 there are some invalid "\r" which makes the mail format invalid and so the headers are not processed correctly on the receiving SMTP server. The result is that the email does not have a subject. I've also tried setting additional headers, but they are all invalid and not processed due to the invalid "\r".
I've tried using both sendmail and ssmtp in the container. It yields the same result.

My php.ini setting are:

sendmail_path = '/usr/sbin/sendmail -t -i -S myserver:25'

Something has changed in the PHP mail() function between PHP 7 and PHP 8

PHP Version

PHP 8.0.14 and newer

Operating System

Docker php:8.0.14-fpm-alpine and php:fpm-alpine

[cmb69]

mail() now outputs proper email line endings (i.e. CRLF instead of LF). It looks like your MTAs convert that to CRCRLF, what would be a bug in those MTAs.

[hansherlighed]

mail() now outputs proper email line endings (i.e. CRLF instead of LF). It looks like your MTAs convert that to CRCRLF, what would be a bug in those MTAs.

The capture from tcpdump is taken on the PHP server, so the trace is captured when going FROM PHP to the MTA(it's the output from sendmail). So the CRCRLF seems to comes from PHP, not the MTA(unless you refer to sendmail as the MTA).
If I read the specifications correctly, PHP should output CRLF directly after each line(which it does in PHP 7.4), but does not in PHP 8.

When you say MTA, do you mean sendmail? Do you mean that it is sendmail that is converting the input from PHP to CRCRLF?
Is there anyway to see the raw output sent from PHP to sendmail?

[cmb69]

You can see the raw PHP output by e.g. writing to a file instead of using sendmail. I.e. set sendmail_path to something like tee mailBasic.out >/dev/null.

[hansherlighed]

Thanks @cmb69

I was able to get the raw output from the mail() function into a file using your advice.
You are indeed right, the raw output from PHP 8 looks like this:

cat -e raw_mailoutput_php8.out

To: redatced@example.com^M$
Subject: This is the subject^M$
^M$
This is the Body^M$

and in PHP 7 it looks like this:

cat -e raw_mailoutput_php7.out

To: redacted@example.com$
Subject: This is the subject$
$
This is the Body$

This issue has actually been reported to PHP way back in 2002:
https://bugs.php.net/bug.php?id=15841
The problem remains the same as reported in this bug. on UNIX systems, the line ending is expected to be "\n" as it is the native line ending for the system. Since PHP's mail() function on UNIX systems, is basically sending raw text output to a UNIX command(sendmail if you follow the documentation) the mail() function will not work as sendmail expects the line endings to be "\n" and NOT "\r\n".
By making this new change to the mail() function so it always uses "\r\n" for the build in headers for Subject: and To:, you've actually made things worse, and made your documentation invalid. It states in the mail() documentation page:

Note:

If messages are not received, try using a LF (\n) only. Some Unix mail transfer agents (most notably [» qmail](http://cr.yp.to/qmail.html)) replace LF by CRLF automatically (which leads to doubling CR if CRLF is used). This should be a last resort, as it does not comply with [» RFC 2822](http://www.faqs.org/rfcs/rfc2822).

Following this note will cause the output from PHP8 to be a mix of "\r\n" and "\n" for the headers. The build in headers for "To:" and "Subject:" will still use "\r\n" even if you set the additional headers to use only "\n".
running mail(redacted@example.com, "This is the subject", "This is the Body", "From: me@example.com\nContent-Type: text/plain"); results in:

cat -e raw_mailoutput_php8.out

To: redacted@example.com^M$
Subject: This is the subject^M$
From: me@example.com$
Content-Type: text/plain^M$
^M$
This is the Body^M$

The essence of the problem is that a UNIX command/program expects line endings to be "\n" and not "\r\n", and since the mail() function on UNIX systems, forwards/outputs to a UNIX command rather than talking to an SMTP server directly, it causes problems.
Why can't the mail() function use the same line endings as PHP_EOL, so that on windows it becomes "\r\n" and unix "\n"? That would make the function more platform independent.

The solution when using the "php:fpm-alpine" image is to set "sendmail_path" to:
'/usr/bin/dos2unix -u|/usr/sbin/sendmail -t -i'