I built the ChatGPT plugin because that is where a lot of people now write their emails. Leaving the chat to run a test, then pasting the findings back in so the model can fix the draft, is exactly the step people skip. With the plugin the report lands in the conversation, and ChatGPT reads it along with you.
Add it to ChatGPT
The plugin has been submitted to the ChatGPT plugin directory and is waiting for review there. Until it is listed you can add it yourself in about a minute, on any plan where ChatGPT lets you connect your own apps:
- In ChatGPT open Plugins, press Add and choose Create MCP App.
- Call it Email Spam Tester and paste
https://email-spam-tester.com/mcpas the server URL. - Set authentication to No authentication, tick the box that you trust the server, and press Create.
Then type @ in a new chat, pick Email Spam Tester, and say what you want to check.
What to ask it
"Check my email for spam problems before I send it." You get a one-hour address in a card with a copy button. Send your draft there from the mailbox or platform you really use, because half of the checks read what that platform adds to the message. The card turns into the report by itself, usually within a minute: the score, the checks that failed or warned, and a fix plan with DNS records ready to paste. A Fix my email button hands the findings to ChatGPT, and it rewrites the draft.
"Test my newsletter and show which folder it lands in at different providers." Same send, with a marker for the subject and one list of recipients to paste into To or BCC. The report then also shows inbox, promotions or spam for each provider, and fills in over the next half hour. Some of those recipients are public test inboxes where the subject and the sender's name are visible, so send a copy with nothing confidential in it.
"Give me a permanent address to track the welcome series of example.com." This one is for mail that arrives in a sequence (a welcome series, a weekly newsletter, order emails). Subscribe the address to your own list and every letter it receives gets the full check. Ask again later and the card lists the letters with their scores, plus the problems that keep coming back from one letter to the next. The address stays the same, and only your ChatGPT account can see what it received.
What it will not do
It does not send email for you and it has no access to your mailbox or to your sending platform. Every test starts with you sending a real message, since a copy sent from somewhere else would tell you about somewhere else.
It also leaves the conversation alone. ChatGPT passes the plugin the few things a tool needs (a report link, a domain, the language you write in) and an anonymous user id, which the server keeps only as a hash. The details, and how long letters are kept, are in the privacy policy.
Outside ChatGPT
The plugin is a plain MCP server, so Claude, Cursor and other clients can use it too; the setup for each is in email-spam-tester-mcp on GitHub. The one-hour test works everywhere. Permanent mailboxes need to know whose they are, and for now only ChatGPT tells the server that. The plugin package itself, with its manifest and review test cases, is in email-spam-tester-chatgpt-plugin.