hooks used in wp_mail suddenly stopped seeing constants after update.

[jmarshall9120]

I'm getting this bug after updating to the latest wp version 5.6.

It looks like my templates that used to work on wp_mail calls have broken. Its odd, because I can get my constants that are declared in wp-config.php from my templates, but they don't seem to be recognized within in the pluggable php core anymore. Have a look at the error:

( ! ) Warning: Use of undefined constant SMTP_FROM - assumed 'SMTP_FROM' (this will throw an Error in a future version of PHP) in C:\xampp\apps\wordpress\htdocs\wp-content\themes\porto-child\functions.php on line 27
Call Stack
#	Time	Memory	Function	Location
1	0.4016	415752	{main}( )	...\index.php:0
2	0.4018	417320	require( 'C:\xampp\apps\wordpress\htdocs\wp-blog-header.php' )	...\index.php:17
3	0.4020	428544	require_once( 'C:\xampp\apps\wordpress\htdocs\wp-load.php' )	...\wp-blog-header.php:13
4	0.4022	446648	require_once( 'C:\xampp\apps\wordpress\htdocs\wp-config.php' )	...\wp-load.php:37
5	0.4027	521712	require_once( 'C:\xampp\apps\wordpress\htdocs\wp-settings.php' )	...\wp-config.php:109
6	0.8790	50953056	do_action( )	...\wp-settings.php:568
7	0.8790	50953432	WP_Hook->do_action( )	...\plugin.php:478
8	0.8790	50953432	WP_Hook->apply_filters( )	...\class-wp-hook.php:311
9	0.9003	51087008	WC_Form_Handler::checkout_action( )	...\class-wp-hook.php:287
10	0.9017	51333928	WC_Checkout->process_checkout( )	...\class-wc-form-handler.php:369
11	1.2388	52568184	WC_Checkout->process_order_payment( )	...\class-wc-checkout.php:1171
12	1.2393	52568560	WC_Gateway_COD->process_payment( )	...\class-wc-checkout.php:959
13	1.2479	52577192	Automattic\WooCommerce\Admin\Overrides\Order->update_status( )	...\class-wc-gateway-cod.php:326
14	1.2583	52562072	Automattic\WooCommerce\Admin\Overrides\Order->save( )	...\class-wc-order.php:333
15	1.2797	52628984	Automattic\WooCommerce\Admin\Overrides\Order->status_transition( )	...\class-wc-order.php:221
16	1.3707	52677736	do_action( )	...\class-wc-order.php:372
17	1.3707	52678112	WP_Hook->do_action( )	...\plugin.php:478
18	1.3707	52678112	WP_Hook->apply_filters( )	...\class-wp-hook.php:311
19	1.3707	52679240	WC_Emails::send_transactional_email( )	...\class-wp-hook.php:287
20	1.3845	53319584	do_action_ref_array( )	...\class-wc-emails.php:170
21	1.3845	53319584	WP_Hook->do_action( )	...\plugin.php:544
22	1.3845	53319584	WP_Hook->apply_filters( )	...\class-wp-hook.php:311
23	1.3845	53320712	WC_Email_New_Order->trigger( )	...\class-wp-hook.php:287
24	1.4179	53456800	WC_Email_New_Order->send( )	...\class-wc-email-new-order.php:98
25	1.4338	53677824	wp_mail( )	...\class-wc-email.php:653
26	1.4366	53681976	apply_filters( )	...\pluggable.php:352
27	1.4366	53682384	WP_Hook->apply_filters( )	...\plugin.php:206
28	1.4366	53683888	set_wp_mail_from( )	...\class-wp-hook.php:287

If I hard code the smtp creds into my functions.php it works. I've also tested on simple templates with out plugins, but this error message seemed the cleanest since it unequivocally shows the include wp-config.php call.

[SergeyBiryukov]

Hi there, welcome to WordPress Trac! Thanks for the report.

The SMTP_FROM constant is not used anywhere in WordPress core, so this appears to be a plugin issue. Please note that this Trac is used for enhancements and bug reporting for the WordPress core software, not for third-party plugins or individual support questions.

The stack trace shows some functions from the WooCommerce plugin, so I would suggest trying their support forums to resolve this: ​https://wordpress.org/support/plugin/woocommerce/.

[jmarshall9120]

@SergeyBiryukov - the SMTP_FROM constant is my constant from my config.php file. It seems wp_mail is no longer seeing the constant's from the config.php file. Is wp_mail not part of core? It is unrelated to any plugin. wp_mail calls broke everywhere they were used in my theme regardless of plugins. The only solution was to hardcode all my constants into the functions.php files hooks for wp_mail.

again I posted the woocommerce stacktrace, because it clearly shows the config.php has been specifically included. Stacktraces with a simple core template are much less verbose.