Verify email addresses in Next.js

// lib/simpleverifier.ts — server code only; never import this from a client component
export type EmailStatus = "valid" | "risky" | "invalid";

const API_URL = "https://simpleverifier.com/api/v1/verify";
const EMAIL_SHAPE = /^[^@\s]+@[^@\s]+\.[^@\s]+$/;

/** Resolves to the verdict, or null when the API could not answer. Never throws. */
export async function emailStatus(email: string): Promise<EmailStatus | null> {
  const address = email.trim();
  if (!EMAIL_SHAPE.test(address)) return "invalid";

  try {
    const res = await fetch(`${API_URL}?email=${encodeURIComponent(address)}`, {
      headers: { Authorization: `Bearer ${process.env.SIMPLEVERIFIER_KEY}` },
      signal: AbortSignal.timeout(30_000),
      cache: "no-store",
    });
    if (!res.ok) return null; // 401, 402, 429, 503: fail open
    const data = (await res.json()) as { status?: EmailStatus };
    return data.status ?? null;
  } catch {
    return null; // timeout or network error: fail open
  }
}

// app/signup/actions.ts
"use server";

import { emailStatus } from "@/lib/simpleverifier";

export interface SignupState {
  ok?: boolean;
  error?: string;
}

export async function signup(_prev: SignupState, formData: FormData): Promise<SignupState> {
  const email = String(formData.get("email") ?? "");
  const status = await emailStatus(email);

  if (status === "invalid") {
    return { error: "This email address cannot receive mail. Please check it." };
  }

  // Save the signup here. status is "valid", "risky" or null (API unavailable).
  return { ok: true };
}

// app/signup/SignupForm.tsx
"use client";

import { useActionState } from "react";
import { signup, type SignupState } from "./actions";

export default function SignupForm() {
  const [state, formAction, pending] = useActionState<SignupState, FormData>(signup, {});

  if (state.ok) return <p>Thanks, you're signed up.</p>;

  return (
    <form action={formAction}>
      <label htmlFor="email">Email</label>
      <input id="email" name="email" type="email" required aria-describedby="email-error" />
      <button type="submit" disabled={pending}>
        {pending ? "Checking…" : "Sign up"}
      </button>
      <p id="email-error" role="alert">
        {state.error}
      </p>
    </form>
  );
}

// app/api/check-email/route.ts
import { NextResponse } from "next/server";
import { emailStatus } from "@/lib/simpleverifier";

export async function POST(request: Request) {
  const body = (await request.json().catch(() => ({}))) as { email?: unknown };
  const email = typeof body.email === "string" ? body.email : "";
  const status = await emailStatus(email);
  return NextResponse.json({ status });
}

{
  "email": "jane@company.com",
  "status": "valid",
  "reason": "Mailbox exists",
  "mailbox_checked": true
}