wp-config.php constants

Every constant below is read once, when the plugin boots — define it in wp-config.php, before /* That's all, stop editing! */. A defined constant always overrides the same value stored in the database; an empty string never overrides a stored value (defined('X') can be true with '').

Connection credentials

A connection’s credentials can be pinned outside the database with a constant named BOOLEANSMTP_{DRIVER}_{KEY} — the driver slug, upper-cased, then the connection setting’s key, upper-cased. For example, a SendGrid connection’s api_key setting becomes:

define( 'BOOLEANSMTP_SENDGRID_API_KEY', 'SG.xxxxxxxx' );

The same rule covers every transport’s credential fields — BOOLEANSMTP_MAILGUN_API_KEY, BOOLEANSMTP_POSTMARK_API_KEY, BOOLEANSMTP_SMTP_USERNAME / BOOLEANSMTP_SMTP_PASSWORD, and so on. Use the wp-config builder below, or read a transport’s exact field names from GET /transports/{driver} on the REST API.

Two legacy aliases are still accepted, for sites that already had them defined before the canonical naming settled:

Constant	Same as	Driver
BOOLEAN_SMTP_USERNAME (no S after BOOLEAN)	BOOLEANSMTP_SMTP_USERNAME	Custom SMTP
BOOLEAN_SMTP_PASSWORD (no S after BOOLEAN)	BOOLEANSMTP_SMTP_PASSWORD	Custom SMTP
BOOLEANSMTP_MICROSOFT_TOKEN	BOOLEANSMTP_OUTLOOK_TOKEN	Outlook (refresh_token / token)

Amazon SES

SES has its own constant set, since its API and SMTP modes take different fields:

// API mode
define( 'BOOLEANSMTP_AWS_SES_ACCESS_KEY_ID', '...' );   // or BOOLEANSMTP_AWS_ACCESS_KEY_ID
define( 'BOOLEANSMTP_AWS_SES_SECRET_KEY', '...' );       // or BOOLEANSMTP_AWS_SECRET_ACCESS_KEY
define( 'BOOLEANSMTP_AWS_REGION', 'us-east-1' );
define( 'BOOLEANSMTP_AWS_SES_CONFIGURATION_SET', '...' );
define( 'BOOLEANSMTP_AWS_SES_CUSTOM_ENDPOINT', '...' );
define( 'BOOLEANSMTP_AWS_SES_ENABLE_V2_API', true );
define( 'BOOLEANSMTP_AWS_SES_STATIC_TAGS', '...' );

// SMTP mode
define( 'BOOLEANSMTP_AWS_SES_SMTP_USERNAME', '...' );
define( 'BOOLEANSMTP_AWS_SES_SMTP_PASSWORD', '...' );
define( 'BOOLEANSMTP_AWS_SES_SMTP_HOST', '...' );
define( 'BOOLEANSMTP_AWS_SES_SMTP_PORT', 587 );
define( 'BOOLEANSMTP_AWS_SES_SMTP_ENCRYPTION', 'tls' );
define( 'BOOLEANSMTP_AWS_SES_SMTP_REGION', 'us-east-1' );

// IAM role source on EC2 (no keys at all)
define( 'BOOLEANSMTP_AWS_ENABLE_IMDS_ROLE_SOURCE', true );
define( 'BOOLEANSMTP_AWS_EC2_IMDSV2_TOKEN_TTL', 21600 );

OAuth redirects (Google, Microsoft, Zoho)

By default, an OAuth connection flow bounces through a central hosted relay so a customer never has to register their own redirect URI with the provider. Three constants change that:

Constant	Effect
BOOLEANSMTP_USE_LOCAL_OAUTH_REDIRECTS	true sends the provider straight back to this site’s own REST callback instead of the relay. Off by default.
BOOLEANSMTP_GOOGLE_OAUTH_REDIRECT_URI	Overrides the redirect URI for the Google flow specifically — for a self-registered Google Cloud app.
BOOLEANSMTP_MICROSOFT_OAUTH_REDIRECT_URI	Same, for Microsoft/Outlook.
BOOLEANSMTP_ZOHO_OAUTH_REDIRECT_URI	Same, for Zoho.

A per-provider constant wins over BOOLEANSMTP_USE_LOCAL_OAUTH_REDIRECTS, which wins over the relay; the boolean_smtp_google_oauth_redirect_uri / _microsoft_oauth_redirect_uri / _zoho_oauth_redirect_uri filters can override any of them.

Behavior

Constant	Effect
BOOLEAN_SMTP_ENCRYPTION_KEY	A dedicated key for encrypting connection credentials at rest, separate from the WordPress auth salts. Changing it after credentials are stored makes them unreadable — export connections first.
BOOLEAN_SMTP_PRESERVE_DATA	true keeps connections, settings and logs in the database when the plugin is deleted, for a later reinstall.
BOOLEAN_SMTP_WP_MAIL_TAKEOVER	Read-only. BooleanSMTP defines this itself, once it confirms it registered wp_mail() successfully — check defined('BOOLEAN_SMTP_WP_MAIL_TAKEOVER') from your own code to know whether it did. Do not define it yourself.

Key rotation

BOOLEAN_SMTP_ENCRYPTION_KEY derives the key that encrypts every stored credential. If you change or remove it after connections exist, BooleanSMTP can no longer decrypt them. Export connections (or note their credentials) before rotating the key, then re-enter them.

Debug logging

Off by default; every channel is opt-in. See debug logging on the user site for what each channel captures.

Constant	Default	Purpose
BOOLEAN_SMTP_DEBUG_HTTP	false	Log outgoing HTTP requests (http_api_debug).
BOOLEAN_SMTP_DEBUG_QUERIES	false	Append database query summaries at shutdown (needs SAVEQUERIES).
BOOLEAN_SMTP_DEBUG_REQUEST	false	Log incoming request metadata.
BOOLEAN_SMTP_DEBUG_MAILER	false	Log payloads from boolean_smtp_api_debug.
BOOLEAN_SMTP_DEBUG_SECRET_VISIBILITY	unset (mask)	mask (default), show (exact values — never on a live site), or full ([REDACTED]).
BOOLEAN_SMTP_DEBUG_REQUEST_SECRET_VISIBILITY	'' (follows global)	Visibility for REQUEST PAYLOAD lines only, independent of HTTP OUT.
BOOLEAN_SMTP_DEBUG_REDACT	false	Legacy: true with no SECRET_VISIBILITY set behaves like full.
BOOLEAN_SMTP_DEBUG_ATTACH_API_DEBUG	false	Legacy opt-in for raw browser diagnostics; prefer the boolean_smtp_api_debug_response_enabled filter.
BOOLEAN_SMTP_DEBUG_LOG_DIR	''	Moves the whole log root (including SMTP debug sessions) to <dir>/boolean-smtp-logs/. Empty uses wp-content/uploads/booleanpress/boolean-smtp/logs.

define( 'SAVEQUERIES', true );              // required for BOOLEAN_SMTP_DEBUG_QUERIES
define( 'BOOLEAN_SMTP_DEBUG_HTTP', true );
define( 'BOOLEAN_SMTP_DEBUG_SECRET_VISIBILITY', 'mask' );

Not for wp-config.php

BOOLEAN_SMTP_FILE, BOOLEAN_SMTP_PATH, BOOLEAN_SMTP_URL, BOOLEAN_SMTP_PLUGIN_FILE, BOOLEAN_SMTP_VERSION, BOOLEAN_SMTP_PRO_VERSION and BOOLEAN_SMTP_VITE_DEV_SERVER(_URL) are set by the plugin itself at boot, for its own internal use. They are documented here only so you recognize them if you see them in a stack trace or wp boolean-smtp output — do not define them.

wp-config builder

Pick a driver and fill in its credentials; copy the define() block it writes. Covers the 5 mailers released today — the same rule applies to any other transport; see REST API: transports for its exact field names.

Copy

Next steps

• REST API — GET /transports/{driver} returns every field a transport’s connection settings accept, if you need a field this page does not list.
• Extending: custom transport — a transport you register yourself reads its own credentials however you write it; these constants only apply to the built-in ones.