add-email-note-to-pmpro-confirmation-message.php

<?php
/**
 * Add a custom message to the confirmation message for specific email domains.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function add_email_note_to_pmpro_confirmation_message( $confirmation_message, $pmpro_invoice ) {

	// Get the email address to check against
	$from_email = get_option( 'admin_email' ); // Change this to the email address you want to check against

	// Array of email domains to check
	$email_domains = array( 'gmail', 'yahoo', 'hotmail' );

	// Get the user ID from the invoice object
	$user_id = $pmpro_invoice->user_id;

	// Get the user object
	$user = get_userdata( $user_id );

	// Get the user email domain without the TLD.
	$email_domain = substr( strrchr( $user->user_email, '@' ), 1 );
	$email_domain = explode( '.', $email_domain )[0];

	// Check if the user email domain matches any domain in the $email_domains array
	if ( in_array( $email_domain, $email_domains, true ) ) {
		// Add a custom message to the confirmation message
		$confirmation_message .= '<p>Please whitelist <strong>' . $from_email . '</strong> in your email client and check your spam folder if the email did not appear in your inbox.</p>';
	}

	return $confirmation_message;
}
add_filter( 'pmpro_confirmation_message', 'add_email_note_to_pmpro_confirmation_message', 10, 2 );