Extending: custom transport

A transport is anything that can configure PHPMailer for a provider and describe its own settings to the admin UI. Every built-in provider — SendGrid, Amazon SES, Custom SMTP, and the rest — is one implementation of TransportContract; a transport you register yourself is no different.

The contract

namespace BooleanSmtp\Contracts;

interface TransportContract
{
    public function getDriver(): string;
    public function getName(): string;
    public function configure(\PHPMailer\PHPMailer\PHPMailer $phpmailer, array $settings): void;
    public function validateSettings(array $settings): array;
    public function getSettingsSchema(): array;
    public function getDeliveryModes(): array;
    public function getSmtpPresets(): array;
    public function getValidationRules(): array;
}

Method	Returns	Purpose
getDriver()	string	The unique driver slug used everywhere else — connection records, wp-config constants, REST routes.
getName()	string	The display name shown in the admin UI.
configure($phpmailer, $settings)	void	Set whatever PHPMailer needs — host, port, API driver — from the decrypted connection settings.
validateSettings($settings)	array<string, string>	Validation errors keyed by field name; empty when valid.
getSettingsSchema()	array<string, array{type, label, required, default?}>	Field definitions the admin UI’s connection form renders from.
getDeliveryModes()	array<string, string>	Delivery modes this transport offers, e.g. ['smtp' => 'SMTP', 'api' => 'HTTP API'].
getSmtpPresets()	array<string, array{host, port, encryption, label}>	Presets shown in the settings dropdown, when relevant.
getValidationRules()	array<string, string>	Pipe-delimited rule strings, e.g. ['api_key' => 'required|string'].

Register it

namespace App\Services\Transport;

use BooleanSmtp\Contracts\TransportContract;

class CustomTransport implements TransportContract {
    public function getDriver(): string { return 'custom'; }
    public function getName(): string { return 'My Custom Provider'; }
    public function configure( \PHPMailer\PHPMailer\PHPMailer $phpmailer, array $settings ): void {
        $phpmailer->isSMTP();
        $phpmailer->Host = 'smtp.example.com';
        $phpmailer->Username = $settings['username'] ?? '';
        $phpmailer->Password = $settings['password'] ?? '';
    }
    public function validateSettings( array $settings ): array { return []; }
    public function getSettingsSchema(): array { return []; }
    public function getDeliveryModes(): array { return [ 'smtp' => 'SMTP' ]; }
    public function getSmtpPresets(): array { return []; }
    public function getValidationRules(): array { return []; }
}

add_filter( 'boolean_smtp_transports', function ( array $transports ): array {
    $transports['custom'] = \App\Services\Transport\CustomTransport::class;
    return $transports;
} );

Once registered, custom behaves like any built-in driver: it appears in GET /transports, a connection can be created with "driver": "custom", and its credentials can be pinned with BOOLEANSMTP_CUSTOM_{KEY} constants — the naming rule is generic, driven by whatever field names your getSettingsSchema() declares.

Next steps

• boolean_smtp_transports — the registration filter itself.
• REST API: transports — GET /transports/{driver} returns exactly what your getSettingsSchema() and getValidationRules() produce.
• Alert channel — the equivalent contract for notification destinations.