I am running into issues when anything in the message requires access control to work. For instance, I have a token that is rendering node content into a message before emailing it.
The problem is that MessageNotifierBase::send() is rendering the view as whichever user happens to be active when it runs. If I send a message interactively using the UI, I get content that is visible to me. If I queue the message to be send on cron, I get only content that is visible to the anonymous user that cron runs as.
When sending mail to a known user in our system, it makes more sense to assume that user's identity when rendering the message to be sure only content that user should see is displayed.
I think this might also fix language problems or other things that depend on knowing who the user is.
The basic idea would be this:
<?php
// Store the current session, it will be anonymous user if run on cron.
// Emulate the permissions of the email recipient.
$accountSwitcher = Drupal::service('account_switcher');
$mail_account = user_load_by_mail($message>getOwnerId());
$needs_switch = FALSE;
// If the message is going to a known, valid, Drupal user, switch accounts.
if (!empty($mail_account) && !$mail_account->isAnonymous()) {
$accountSwitcher->switchTo($mail_account);
$needs_switch = TRUE;
}
// Render the content here.
// Revert back to original user.
if ($needs_switch) {
$accountSwitcher->switchBack();
}
?>