Email Being Sent From php Mail from address.

Maybe you forgot to specify the From address in the additional headers and additional parameters?

The php mail() function is this:

bool mail ( string $to , string $subject , string $message [, string $additional_headers [, string $additional_parameters ]] )

Usually, you need to do two things:

1) in the $additional_headers, include the From: address

2) in the $additional_parameters, include the "-f address" parameter

For example:

// Required variables
$FROMEMAIL  = "from@me.com";
$TOEMAIL    = "to@you.com";
$SUBJECT    = "my email subject";
$PLAINTEXT  = "body of email in plain text";
$RANDOMHASH = "whatever";

// Basic headers
$headers = "From: ".$FROMEMAIL."\n";
$headers .= "Reply-To: ".$FROMEMAIL."\n";
$headers .= "Return-path: ".$FROMEMAIL."\n";
$headers .= "Message-ID: <".$RANDOMHASH."@myserver.tld>\n";
$headers .= "X-Mailer: My Application Name\n";
$headers .= "MIME-Version: 1.0\n";

// Add content type (plain text encoded in quoted printable, in this example)
$headers .= "Content-Type: text/plain; charset=UTF-8\nContent-Transfer-Encoding: quoted-printable\n";

// Convert plain text body to quoted printable
$message = quoted_printable_encode($PLAINTEXT);

// Create a BASE64 encoded subject
$subject = "=?UTF-8?B?".base64_encode($SUBJECT)."?=";

// Send email
mail($TOEMAIL, $subject, $message, $headers, "-f".$FROMEMAIL);

Thanks for your response ifThenElse.

I don't think this is being caused by the code as I have used this plugin on many occasion and it has always used the settings you create. I think this is more to do with the Linode set-up. It's a while since I set up my Linode but I do recall a setting at some point specifying localhost.localdomain but I can't remember where. So I think it is this setting that is being used in php mail is there somewhere in the Linode setup that you specify a mailing domain perhaps?

In CentOS 7, you set the hostname (FQDN more specifically) with the following command:

hostnamectl set-hostname myhost.whatever.tld

Just make sure you have a local MTA like postfix, check with:

systemctl status postfix

By default, PHP uses the command /usr/sbin/sendmail -t -i to transmit mail, which in turn points to /etc/alternatives/mta, which can be used with postfix, exim or other MTA that you've previously setup.

Also, make sure you haven't placed the hostname of the server in the wrong place, like in /etc/hosts, it should NOT point to 127.0.0.1 or localhost.localdomain.