export declare namespace ClientOptions {
    /**
     * Custom fetch implementation signature.
     *
     * Node's built-in fetch (undici) does not read HTTP_PROXY/HTTPS_PROXY/NO_PROXY. Supplying a
     * custom fetch (for example one bound to an undici ProxyAgent dispatcher) is the supported way
     * to route requests through a corporate egress proxy or otherwise customise transport.
     */
    type FetchImplementation = (input: RequestInfo | URL, init?: RequestInit) => Promise<Response>;
    class Configuration {
        useHttps?: boolean;
        requestHost?: string;
        timeout?: number;
        fetch?: FetchImplementation;
        constructor(useHttps?: boolean, requestHost?: string, timeout?: number, fetch?: FetchImplementation);
    }
    enum HttpMethod {
        GET = "GET",
        POST = "POST",
        DELETE = "DELETE",
        PUT = "PUT",
        OPTIONS = "OPTIONS",
        HEAD = "HEAD",
        PATCH = "PATCH"
    }
    enum AuthHeaderNames {
        SERVER_TOKEN = "X-Postmark-Server-Token",
        ACCOUNT_TOKEN = "X-Postmark-Account-Token"
    }
}