1 system.api.php hook_mail_alter(&$message)

Alter an email message created with the backdrop_mail() function.

hook_mail_alter() allows modification of email messages created and sent with backdrop_mail(). Usage examples include adding and/or changing message text, message fields, and message headers.

Email messages sent using functions other than backdrop_mail() will not invoke hook_mail_alter(). For example, a contributed module directly calling the backdrop_mail_system()->mail() or PHP mail() function will not invoke this hook. All core modules use backdrop_mail() for messaging, it is best practice but not mandatory in contributed modules.


$message: An array containing the message data. Keys in this array include:

  • 'id': The backdrop_mail() id of the message. Look at module source code or backdrop_mail() for possible id values.
  • 'to': The address or addresses the message will be sent to. The formatting of this string must comply with RFC 2822.
  • 'from': The address the message will be marked as being from, which is either a custom address or the site-wide default email address.
  • 'subject': Subject of the email to be sent. This must not contain any newline characters, or the email may not be sent properly.
  • 'body': An array of strings containing the message text. The message body is created by concatenating the individual array strings into a single text string using "\n\n" as a separator.
  • 'headers': Associative array containing mail headers, such as From, Sender, MIME-Version, Content-Type, etc.
  • 'params': An array of optional parameters supplied by the caller of backdrop_mail() that is used to build the message before hook_mail_alter() is invoked.
  • 'language': The language object used to build the message before hook_mail_alter() is invoked.
  • 'send': Set to FALSE to abort sending this email message.

See also


Related topics


core/modules/system/system.api.php, line 1466
Hooks provided by Backdrop core and the System module.


function hook_mail_alter(&$message) {
  if ($message['id'] == 'modulename_messagekey') {
    if (!example_notifications_optin($message['to'], $message['id'])) {
      // If the recipient has opted to not receive such messages, cancel
      // sending.
      $message['send'] = FALSE;
    $message['body'][] = "--\nMail sent out from " . config_get('system.core', 'site_name');