Add filter to emails sent by wp-admin/network/site-new.php

[johnbillion]

wp-admin/network/site-new.php contains a call to wp_mail() which sends an email when a new site is created from Network Admin -> Sites -> Add New on Multisite. (Ref).

The contents of the email cannot be filtered. The recipient, subject, message, and headers should be passed through a filter in the same format as the password_change_email filter. (Ref).

[johnbillion]

Related: #42135

[Dhruvin]

Added a filter for filtering the contents of the email sent when a new site is created.

[Dharm1025]

better patch with placeholders and some other improvements

[dharmin16]

added the feature simmilar to wp_welcome_message(). E.g. Filter 'wpmu_admin_notification' to disable or bypass. Filter 'update_admin_notification' and 'update_admin_notification_subject'} to modify the content and subject line of the notification email.

[desrosj]

These patches need to be reviewed and tested.

[jipmoors]

Looking at the code I'm seeing some places that can be improved. As this is a stand-alone function better checking for unexpected situation will improve functionality.

• get_userdata can return unexpected data, as the user ID doesn't have to be valid
• $admin_notification is being determined using a filter, which can return an empty value; an email should not be send if there is no message

Site tite:
Title is being provided as an argument to the function, but $current_network->site_name is being used instead.
In this implementation $current_network->site_name is being set to a value, this might have unwanted side-effects.

Some other concern I noticed:
The admin_email will be default in this patch to: 'support@' . $_SERVER['SERVER_NAME']
But support is not a default emailbox. Suggesting to use "postmaster" or even considering of returning a WP_Error and not sending an email at all.

[desrosj]

This still needs some work. With 5.3 beta 1 in a few hours, it needs to be punted.

[johnbillion]

#42135 was marked as a duplicate.

[johnbillion]

42134.diff​ continues on from the patches here and on #42135.

• Improved naming and structure of the filters
• Avoid passing unnecessary parameters such as the site title, as this can be gotten from the site option
• Pass the complete site and user objects to the filters
• Correctly switch to the locale of the user associated with the network admin email address, falling back to the locale of the site if there isn't one

This is looking good to me now.

[johnbillion]

In 49127:

Networks and Sites: Extract into a new function the email that gets sent to the network administrator when a new site is created, and introduce filters to disable and modify its

contents.

• The send_new_site_email filter can be used to disable this email.
• The new_site_email filter can be used to modify its contents.

Props Dhruvin, Dharm1025, dharmin16, jipmoors

Fixes #42134

[SergeyBiryukov]

In 49130:

Docs: Correct comments in wpmu_new_site_admin_notification() per the documentation standards.

See #42134.

[desrosj]

Let's note this new filter in the miscellaneous dev note.

[daisyo]

Dev note published: ​https://make.wordpress.org/core/2020/11/20/miscellaneous-developer-focused-changes-in-wordpress-5-6/

[dharmin16]

#44781 was marked as a duplicate.