Domain Mail Check in VS Code

Questions it answers

Check how a domain is set up for email, whether Gmail and Outlook are likely to accept its mail, and who it is registered with, from public DNS, free blocklists and registry data.

Ask "will Gmail accept mail from example.com sent from 203.0.113.7?", "is DMARC set up correctly for github.com?", "check SPF and DKIM for example.com", "which mail provider does acme.io use?" or "when does openai.com expire?".

The email check reads the domain's SPF record (following include and redirect, counting DNS lookups against the limit of 10), its DMARC policy, the MX records and, when you give a DKIM selector, whether the DKIM key is published. It returns a grade from A to F for protection against spoofing, the problems it found and a short list of fixes. The DNS records tool reads A, AAAA, MX, TXT, CAA and NS records with their TTLs, which also shows which mail provider a domain uses and which certificate authorities may issue for it. The registration tool reads the domain's registry record over RDAP: registrar, creation and expiry dates, status flags and name servers.

The delivery check gives one verdict for Gmail and Outlook, the top 3 causes and one fix for each. It tests the published sender rules (SPF listing the sending IP, DKIM, DMARC, reverse DNS of the IP, key length) and reads 6 free blocklists (SpamCop, PSBL, UCEPROTECT level 1, Mailspike and NordSpam for the IP and the domain). Each rule and each list names its official source.

The cold-email launch score gives a score from 0 to 100 for a new sending domain, with a verdict of ready, almost or not_ready and the 5 fixes to make first. It tests SPF, DKIM, DMARC, reply mail, a domain blocklist, the domain's age from the registry record and the shape of its name. Each rule names its source and is labelled standard (a published requirement) or opinion (common advice nobody requires, which never decides not_ready).

DNS answers come from Cloudflare's DNS over HTTPS service with Google Public DNS as a fallback, and registration data from the registry of the domain's ending, found through IANA's RDAP directory. Every answer names its source and the date it was read.

It does not send a test message or read mailboxes, so a good verdict means no published rule is broken, not a promise of the inbox; it does not read sender reputation, find subdomains, or return who owns a domain: registrant and contact details are never read or returned. It checks the exact domain you give, so a parent domain's SPF or DMARC record is not inherited. The domains you ask about are not stored; the only lasting record is a daily count of calls per tool.

Short questions this server answers, each with a direct answer: Email SPF, DKIM, DMARC and Domain Expiry Check.

The idea behind it, in one live picture: how Domain Mail Check works.

What it can do

• Reads a domain's SPF record, counts its DNS lookups and flags weak or broken policies
• Reads the DMARC policy, percentage and report address
• Checks whether DKIM keys are published for up to 5 selectors you name
• Grades email spoofing protection from A to F with a short list of fixes
• Reads A, AAAA, MX, TXT, CAA and NS records with TTLs and names the mail provider from the MX records
• Shows registrar, creation and expiry dates, status flags and name servers from the registry over RDAP
• Never returns registrant or contact details; names its sources and dates
• Gives one verdict on whether Gmail and Outlook will likely accept the domain's mail, the top 3 causes and one fix each
• Checks SPF for the sending IP, reverse DNS, DKIM key length and DMARC against the Gmail, Yahoo and Outlook rules
• Reads 6 free blocklists for the domain and the sending IP, with each list's terms link
• Scores a cold-email sending domain 0 to 100 from SPF, DKIM, DMARC, domain age and name, with fixes
• Labels each rule standard or opinion and links its source, so advice is not shown as a requirement

Tools

• launch_score, Score a cold-email domain. Use this when the user asks whether a new or secondary domain is ready for cold email or outreach, or wants a score for a sending domain, such as "is acme-mail.com ready for cold email?". Pass the domain and, optionally, up to 5 DKIM selectors. Returns a score from 0 to 100, a verdict (ready, almost, not_ready or incomplete), the 5 fixes to make first, every rule with its status, its kind (standard for a published requirement, opinion for common advice nobody requires) and its source link, the domain's registration date and age, what was not tested, and the source and as_of date. Opinion rules change the score but can never make the verdict not_ready. It reads public DNS and the public registry record only: it sends no message and cannot see sender reputation or warm-up, so it does not promise inbox placement.
• delivery_check, Check mail delivery. Use this when the user asks whether mail from a domain will reach Gmail or Outlook, or why it is rejected or goes to spam, such as "will Gmail accept mail from example.com sent from 203.0.113.7?". Pass the domain, the sending IPv4 address if known, the return-path domain (mail_from) if known and, optionally, up to 5 DKIM selectors. Returns one verdict (likely_accepted, at_risk, likely_rejected or incomplete) with a verdict per provider, the top 3 causes each with one fix, the exact SPF and DMARC records to paste (records_to_paste) and the DKIM steps for the detected mail provider (fix_steps), every rule checked with its official source link (SPF for the IP, DKIM, DMARC, reverse DNS, blocklists), the 6 blocklists with their terms links, what was not checked, and the source and as_of date. Gmail and Outlook are always both reported, so there is no provider argument. It reads public DNS and free blocklists only: it sends no test message and cannot see sender reputation, so it does not promise inbox placement.
• check_email_auth, Check email authentication. Use this when the user asks whether a domain's email is set up correctly, such as "is DMARC set up for github.com?" or "check SPF and DKIM for example.com". Pass the domain and, if known, up to 5 DKIM selector names. Returns SPF (policy, DNS lookup count, issues), DMARC (policy, percentage, report address, issues), DKIM per selector, the MX hosts and mail provider, a grade from A to F, a list of fixes, the exact SPF and DMARC records to paste (records_to_paste) and the DKIM steps for the detected mail provider (fix_steps), the source and as_of date, and a page link that shows the same check on the web. It reads public DNS only: it does not send mail, test delivery or read mailboxes.
• check_dns_records, Look up DNS records. Use this when the user asks for a domain's DNS records, its mail provider or which certificate authorities may issue for it, such as "which mail provider does acme.io use?" or "show the MX and CAA records for github.com". Pass the domain and optionally up to 6 record types from A, AAAA, MX, TXT, CAA and NS (default: all). Returns each type's records with TTL, the mail provider named by the MX hosts, and the source and as_of date. It reads public DNS only; it cannot list subdomains or other record types.
• lookup_domain_registration, Look up domain registration. Use this when the user asks who a domain is registered with or when it expires, such as "when does openai.com expire and who is the registrar?". Pass the domain. Returns whether it is registered, the registrar, creation, update and expiry dates, days until expiry, registry status flags, name servers, and the source and as_of date. Registrant and contact details are never returned, so it cannot say who owns a domain.

Add Domain Mail Check in VS Code

VS Code reads MCP servers from mcp.json and offers their tools to Copilot Chat in Agent mode. A workspace file at .vscode/mcp.json applies to that project. For every workspace, run MCP: Open User Configuration from the Command Palette and add the same entry there. These steps were checked against the VS Code MCP servers guide on 2026-10-09.

Create or edit the file so it contains this server. VS Code uses a top-level servers object, not mcpServers. Merge it with servers you already have.

{
  "servers": {
    "mailcheck": {
      "type": "http",
      "url": "https://mailcheck.openkrill.app/mcp"
    }
  }
}

No command, no headers and no input variables for a key: Domain Mail Check answers without a login. Save the file and select Start above the entry. VS Code asks once whether you trust the server: confirm it. Run MCP: List Servers to check that Domain Mail Check is running. You should see launch_score, delivery_check, check_email_auth, check_dns_records, lookup_domain_registration.

Open the Chat view, choose Agent mode and ask: Is DMARC set up correctly for github.com? The Configure Tools button in the chat input lists the tools of each server, and VS Code may ask you to confirm the first call. The server is public and read-only. It sees only the arguments of each call, so do not paste secrets into the question.

Command line users can add it to the user profile in one step with code --add-mcp and the same name, type and url as JSON. The portable .mcp.json at the project root also works in VS Code, with mcpServers as its top-level key. An organization can turn MCP off through Copilot policy: if the MCP commands are missing, ask the admin.

If it does not work

A call checked on 2026-10-11

github.com publishes SPF and DMARC. The grade is a reading of those records, not a security audit. The request below was posted to https://mailcheck.openkrill.app/mcp as tools/call. HTTP 200. Source: the Domain Mail Check server, read 2026-10-11.

{
  "method": "tools/call",
  "params": {
    "name": "check_email_auth",
    "arguments": {
      "domain": "github.com"
    }
  }
}

• status. ok
• grade. A
• as of. 2026-10-11
• source. Cloudflare DNS over HTTPS (cloudflare-dns.com)
• notice. Checks the exact domain given: SPF and DMARC records of a parent domain are not inherited here. The grade rates protection against spoofing only; it does not read mail or test delivery, and DKIM needs a selector name fro
• dkim status. unknown

Repeat the call yourself if you need a newer reading. Cached answers expire. A rate limit is not a result: wait and try again. Nothing in the call is a ranking, a filing, or advice.

Using it in production

Nothing to install and nothing to run: no package, no Python or Node.js version and no environment variable. Domain Mail Check runs on our servers, and your client only needs the URL https://mailcheck.openkrill.app/mcp.

Use it in other apps

• Domain Mail Check in ChatGPT
• Domain Mail Check in Claude
• Domain Mail Check in Cursor
• Domain Mail Check in Pi

Roles that use Domain Mail Check

• Startup founder guide

Frequently asked questions

Words on this page

• MCP (Model Context Protocol) definition
• Streamable HTTP transport definition
• Tool primitive definition
• Rate limit policy definition

Source: plugin listing for mailcheck in this repository, and a live tools/call on 2026-10-11. As of 2026-10-11.