/**
 * Options for {@link injectPreheader}.
 */
interface PreheaderOptions {
  /**
   * Append invisible padding characters so the preheader text isn't followed by leaked body content
   * in the inbox preview.
   * @default true
   */
  spacer?: boolean;
}
/**
 * Injects a hidden preheader (inbox preview text) at the start of the HTML body.
 *
 * The preheader is wrapped in a `display:none` element with `mso-hide:all`, followed by zero-width
 * padding so the preview shows only your text. Inserted right after `<body>` (or prepended if no
 * body tag is present).
 * @param html The HTML email.
 * @param preheader The preview text.
 * @param options Injection options. See {@link PreheaderOptions}.
 * @returns The HTML with the preheader injected.
 */
declare const injectPreheader: (html: string, preheader: string, options?: PreheaderOptions) => string;
export { PreheaderOptions, injectPreheader };