Add: MAIL_ENVELOP_FROM constant for flexible email Sender header mana…

[nzsys]

Summary

This pull request introduces a new MAIL_ENVELOP_FROM constant to allow better control of the "Sender" header in outgoing emails.

Why is this important ?
Using a properly configured sender email is essential for meeting SPF / DKIM requirements, improving deliverability, and avoiding spoofing issues.

To adopt this feature, users can define the MAIL_ENVELOP_FROM constant in wp-config.php.This configuration is especially beneficial in multisite environments, where dynamic Sender values may be needed.

Changes

Core logic changes
Updatedwp-includes/pluggable.php to set PHPMailer’s Sender property based on the MAIL_ENVELOP_FROM constant(if defined).
Added tests to cover cases where MAIL_ENVELOP_FROM is defined and where it is not.

Why

The "Sender" header is critical for the following reasons:

• SPF and DKIM Authentication
  Ensures emails are not flagged as spoofed by third parties.Accurate and consistent Sender addresses are necessary to meet the requirements for SPF and DKIM authentication.

• Flexible Control
  Site - specific email addresses can be used for better brand consistency, or notification emails can be configured to meet the requirements of particular domain forwarding servers.

Usage

Single Sites

For most single - site configurations, theMAIL_ENVELOP_FROM constant can be defined in wp-config.php as follows:

/**
 * Envelope-from email address for outgoing WordPress emails.
 * Example: Replace [email protected] with a real email address
 * that has SPF/DKIM properly configured for your domain.
 */
define('MAIL_ENVELOP_FROM', '[email protected]');

Multisite Configurations

if (str_contains($_SERVER['HTTP_HOST'], 'site1.com')) {
	define('MAIL_ENVELOP_FROM', '[email protected]');
} elseif(str_contains($_SERVER['HTTP_HOST'], 'site2.com')) {
	define('MAIL_ENVELOP_FROM', '[email protected]');
} else {
	define('MAIL_ENVELOP_FROM', '[email protected]');
}

This setup allows you to handle different sender addresses based on the site or subdomain.

Impact

This change enables more flexible management of the sender email address, making it easier to improve email delivery reliability and SPF / DKIM authentication success rates.This is particularly useful for multisite or complex email environments, as it helps address challenges with sender configuration.

[github-actions]

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[github-actions]

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[github-actions]

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[github-actions]

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[ocean90]

Noting that you can already change the sender by using the phpmailer_init action, see this example. There doesn't seem to be a need for a new constant which isn't as flexible as a hook.

[nzsys]

Thank you for your feedback. I understand that the sender can be changed using the phpmailer_init hook. However, since this is a theme or plugin-level setting, it may not be sufficient to ensure consistency across the entire site.

Therefore, I believe allowing this to be configured in wp-config.php would be more appropriate, as it ensures consistency at the software level (across WordPress) and makes it easier to manage.