Fixed email header bug which would become a major issue with PHP8

application/Emailnotification/Emailnotification.php

@@ -122,6 +122,18 @@ class Emailnotification {
     //$log->debug(print_r($headers, true));
     
     $mail =& Mail::factory('mail', ["-f ".$this->email_from]);
+    /*
+     * PHP 8's mail() function now outputs proper line endings in headers (CRLF instead of LF).
+     * Mail_mail < 2.0 would detect a unix system and change the headers line ending to LF.
+     * On Mail submission to Exim (via sendmail), mail() adds its own headers first with CRLF line ending,
+     * making Exim treat every subsequent header's LF as an invalid line ending, adding a whitespace after the LF,
+     * making all our custom headers into one long header.
+     *
+     * See: https://www.exim.org/exim-html-current/doc/html/spec_html/ch-message_processing.html#SECTlineendings
+     *
+     * So we force CRLF line endings for headers here.
+     */
+    $mail->sep = "\r\n";
     $mail->send($this->email_to, $headers, $body);
   }