Incompatibility with mail plugin

  • I’m using this plugin on a site where PostSMTP is used to send mails more reliably. HTTP Headers stops the plugin from using its own mailing function.

    Postman: wp_mail has been declared by another plugin or theme, so you won't be able to use Postman until the conflict is resolved.
    More info that may help - /[...]/wp-includes/pluggable.php:174

    Here’s what I think is happening after a bit of research:

    PostSMTP checks function_exists ('wp_mail') in post-smtp/Postman/PostmanWpMailBinder.php before defining the function with their own mailing code. The standard WordPress mailing function does the same in wp-includes/pluggable.php, so if no plugin defines wp_mail with their own code before pluggable.php, the standard function is declared.

    However, HTTP Headers seems to load pluggable.php before PostSMTP runs, so it defines the standard wp_mail and PostSMTP cannot overwrite it. This happens in http_headers_option($option) in http-headers.php:

    require_once ABSPATH . WPINC . '/pluggable.php';

    Is this something you can fix or provide a workaround for? Thanks!

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