--- title: "Test sign-up emails in apps built with OpenAI Codex · Proxy Mail QA" description: "OpenAI Codex can implement sign-up, login and password reset for you. Here's how to run the real email flow before you merge, with a private test inbox and instant codes." url: https://proxymail.qa/built-with/codex --- 1. [Home](https://proxymail.qa/) 2. [AI app builders](https://proxymail.qa/built-with) # Testing auth emails in apps you build with OpenAI Codex Codex can implement a sign-up or password-reset flow and hand you a ready-to-review change. Before you merge it, run the real email path once: it's the part tests rarely cover. ## Add to Codex [ Proxy Mail QA pluginFor Codex and ChatGPT, in ChatGPT’s plugin directory: Try in chat (opens in a new tab)](https://chatgpt.com/plugins/plugin%5Fasdk%5Fapp%5F6acde757c5748191af402b25494ad875) Sign in to Proxy Mail QA when it asks and choose the project it may use. Free, with no API key to copy. The Codex IDE extension doesn’t take plugins: its one-line setup is further down. [Other ways to connect ](https://proxymail.qa/built-with/codex#let-codex-check-the-email-itself) Updated 29 October 2026 ## Why the email path needs a human check Codex is OpenAI’s coding agent. You can use it from the terminal, from your editor, or hand it tasks to work on in the cloud and review the result. It’s good at the code around authentication: forms, API routes, token handling and templates. But a change can pass every test and still send an email that links to the wrong place, never arrives because the sender isn’t configured, or uses a code that expires before anyone could type it. Those only show up when a real email reaches a real inbox. ## Which login will it build? Whichever your app already uses, or the one you ask for. Supabase Auth, Clerk, Firebase Authentication, Auth.js and Better Auth each send different emails, and each has one setting that breaks them most often. Name the methods you want in the task, such as “email and password with a confirmation code, plus Google”, so the change and your check cover the same emails. [Which emails each login service sends](https://proxymail.qa/built-with/login-methods#login-services-coding-agents-use). ## Check it before you merge 1. **Run the branch.** Start it locally, or open the preview deployment if your host creates one for each change. 2. **Create an address** in Proxy Mail QA and sign up, request a magic link or reset a password: whatever the change touched. 3. **Use the code or link from the row.** The code has a **Copy** button; links become a button named for what they do. 4. **Read the whole email once.** Check the sender, subject, wording and every link in the inbox view. 5. **Note what you found** on the address, so it travels with the test account. If the link points at `localhost` on a preview or staging deployment, it’s flagged. That usually means a hard-coded URL or a missing environment variable: [see the fixes](https://proxymail.qa/solve/localhost-links). ## Let Codex check the email itself Install the [Proxy Mail QA plugin](https://chatgpt.com/plugins/plugin%5Fasdk%5Fapp%5F6acde757c5748191af402b25494ad875) from ChatGPT’s plugin directory: it works in Codex and in ChatGPT. Sign in to Proxy Mail QA in your browser when it asks and choose the project it may use, with no API key to copy. The Codex IDE extension doesn’t take plugins. To add the MCP server there, run this in a terminal: Terminal ```bash codex mcp add proxymail-qa --url https://api.proxymail.qa/mcp ``` Codex opens your browser to sign in; if it doesn’t, run `codex mcp login proxymail-qa`. The Codex CLI, the IDE extension and the ChatGPT desktop app share this setting. To use an API key instead, see [MCP server setup](https://proxymail.qa/docs/mcp#openai-codex). Then ask in plain words: “Sign up on localhost:3000 with a new Proxy Mail QA address and confirm the email.” Codex creates the address, fills in your form, waits for the code or link and finishes the sign-up. It gets only the code or link, never the email’s text. ## Turn findings into the next task Give Codex a precise follow-up rather than “email is broken”: - “On preview deployments the verification link uses `http://localhost:3000`. Read the base URL from an environment variable.” - “The code email says 10 minutes but the server rejects codes after 2\. Make them match.” - “Requesting a new magic link should invalidate the previous one.” ## Tips - **One address per scenario.** Create a small batch, each with a generated name and username, for new user, invited user and reset tests. - **Plus tags for repeated runs.** `name+pr482@mailclub.dev` arrives in `name@mailclub.dev`, with the tag shown. - **Save the password.** Keep the password you signed up with on the same row, encrypted and hidden until you need it. ## Try it on your next sign-up test Free plan, no credit card. Create an address and watch the code or link arrive. [Create a free account](https://app.proxymail.qa/?mode=signup&from=codex) ## Questions ### Codex tasks run in a sandbox. Where do I test the email? Wherever your app actually runs and sends mail: your own machine, a preview deployment or staging. The sandbox is where the code is written; the email check happens on a running copy of the app. ### Can Codex read the code from the email itself? Yes. Install the Proxy Mail QA plugin from ChatGPT's plugin directory and sign in through your browser. In the Codex IDE extension, which doesn't take plugins, add the MCP server with codex mcp add proxymail-qa --url https://api.proxymail.qa/mcp instead. Then Codex can create an address, sign up and wait for the code or link. See proxymail.qa/docs/mcp. ### Do I need to change my app? No. Sign up with a Proxy Mail QA address like any user. Your email provider delivers to it like any other inbox, as long as it isn't in sandbox or test mode, which only sends to addresses you've verified. ## Related guides - [LovableWhich Lovable Cloud logins send email, the Site URL and sender settings, and a check before you launch.](https://proxymail.qa/built-with/lovable) - [ReplitReplit Auth, Clerk Auth or your own: which send email, and how to test each on the published app.](https://proxymail.qa/built-with/replit) - [BoltTurn on email confirmation, fix the localhost Site URL and test every auth email before you publish.](https://proxymail.qa/built-with/bolt) - [Base44Test the sign-up code, password reset and invites, and every user role, with a test account per role.](https://proxymail.qa/built-with/base44) - [v0Set Supabase’s Site URL and redirects for Vercel deployments, or move Clerk to production, then test every login email.](https://proxymail.qa/built-with/v0) - [Claude CodeCheck the auth emails in apps you build with Anthropic’s coding agent, from localhost to staging.](https://proxymail.qa/built-with/claude-code) - [QoderCheck the real sign-up, code and reset emails after the agent changes your auth code, or let it check them itself.](https://proxymail.qa/built-with/qoder) - [CursorCheck the real sign-up, magic-link and reset emails after the agent changes your auth code.](https://proxymail.qa/built-with/cursor) - [Google AntigravityKeep unverified Firebase users out, check authorized domains and the sender, and let the agent run the check.](https://proxymail.qa/built-with/antigravity) - [Login methods explainedEmail, codes, magic links, Google and Apple buttons, phone and SSO: what each sends, what breaks and how to test it.](https://proxymail.qa/built-with/login-methods) [See every email testing problem we solve](https://proxymail.qa/solve) Codex is a product of OpenAI. OpenAI, Codex, ChatGPT and the OpenAI logo are OpenAI’s trademarks. Proxy Mail QA is independent and isn’t affiliated with or endorsed by them.