Modify wp_installed_email / wp_new_blog_notification

Question

When WordPress is installed, it sends a notification

New WordPress Site
Your new WordPress site has been successfully set up at:
...

I would like to change the text of the e-mail but am not successfull. Here is what I tried:

I added the following code to the main file of a plugin which I add before the installation

function changed_install_mail($installed_email, $user, $blog_title, $blog_url, $password ) {
    $installed_email['subject'] = 'test';
    return $installed_email;
}
add_filter( 'wp_installed_email', 'changed_install_mail', 10, 5 );

I tried to play around with the priority, but the filter never gets added. But other code in this plugin file is executed.

This filter gets applied in upgrade.php

$installed_email = apply_filters( 'wp_installed_email', $installed_email, $user, $blog_title, $blog_url, $password );

Maybe it's the wrong time or wrong location I'm trying it?

Answer 1

I found a solution: mu-plugins. My code isn't executed in this early state, but that's what mu-plugins are for. https://wordpress.org/support/article/must-use-plugins/ This did the trick.

Answer 2

just an opinium, each wordpress plataform is only instaled one time, and each time only the email registered will receive the email. Not my business, but isnt this worthless, if the person is installing wordpress, he knows the wordpress is being installed. if some other email is being their instead of the one who is installing it, why just not send a personal email giving the information. Also if you personalize one wordpress files to do so, you will need to use that files always you install a new wordpress. Also update your files each time wordpress has a new release/update. I must confess, I have installed a few and never had receive such email. And for the email to work always had to put some code on the theme functions.php