Which ESP sent this email? Find the sending platform from the headers
To find which email service provider sent a message, read its headers. This tool does it in your browser: it checks the DKIM signing domain, the Return-Path bounce domain, the sending side of the Received chain, headers platforms add (such as X-SG-EID for SendGrid) and the unsubscribe link, and names the platform with the lines that show it.
Sample result
This newsletter from acme.example was sent with SendGrid.
- Sent with
- SendGrid
- From
- acme.example
- Also signed by
- acme.example
What this means for you
Three header lines point at SendGrid: its DKIM signature, its X-SG-EID header and its unsubscribe link.
- DKIM d=, Return-Path and Received chain
- Platform headers like X-SG-EID, X-Mailgun-Sid
- Ignores the recipient's own servers
- Paste headers or upload an .eml file
- ESP
- Headers
- DKIM
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
How do I find out which email platform sent a message?
- Open the email and copy its raw headers: in Gmail, More then Show original; in Outlook, File then Properties; in Apple Mail, View then Message then All Headers.
- Paste them here, or upload the saved .eml file.
- Press Find the sending platform. Nothing is uploaded; the headers are read in your browser.
- Read the sending platform and every line of evidence, plus any other services that handled the message.
Example
- You enter
- The raw headers of a newsletter from
news@acme.example, DKIM-signed byacme.exampleandsendgrid.net, with anX-SG-EIDheader and an unsubscribe link onct.sendgrid.net. - You get
- Sending platform SendGrid, from three lines: DKIM-Signature d=sendgrid.net, the X-SG-EID header and the List-Unsubscribe host. acme.example is listed as another DKIM signer; the bounce domain is
em4821.acme.example. - Limits
- Runs in your browser with no limit; paste headers or upload an .eml file. Nothing is uploaded.
How do you tell which platform sent an email?
Every sending platform leaves traces. Most sign with DKIM, and unless the sender has set up a custom signing domain, the d= tag is the platform's own domain (d=sendgrid.net, d=mcsv.net for Mailchimp, d=amazonses.com). Bounces usually go to a platform-owned Return-Path domain. The Received lines show the servers the message passed through, and some platforms add their own headers: X-SG-EID (SendGrid), X-Mailgun-Sid (Mailgun), X-SES-Outgoing (Amazon SES), X-PM-Message-Id (Postmark), X-MC-User (Mailchimp).
The tool only reads the sending side of the Received chain, up to the hop where the message crossed to the recipient's provider, so the recipient's own servers (Gmail receiving your mail, for example) aren't mistaken for the sender.
Why does it say no platform was found?
Large senders often set a platform up fully on their own domain: a custom DKIM domain, a branded bounce domain and branded link tracking. Then the headers only show the company's domains. The tool lists those other DKIM signers so you can look the domain up in the email stack lookup, which reads its SPF and DKIM DNS records for the platforms behind them.
Is it safe to paste email headers?
The headers stay in your browser; nothing is sent to our server. They do contain addresses and server names, so if you share them anywhere else, remove what you don't want seen. The message body isn't needed.
How is this different from an email header analyzer?
| ESP detector | Header analyzer | |
|---|---|---|
| Answers | Which platform sent it? | Did it pass SPF, DKIM and DMARC, and where was it delayed? |
| Reads | DKIM d=, Return-Path, Received, platform headers | Every hop, authentication result and spam header |
| Best for | Competitor and prospect research | Debugging delivery |
Who uses this tool, and for what?
- Marketers
- See which platform a competitor's newsletter or a campaign you admire was sent with.
- Sales teams
- Learn a prospect's email platform from a message they sent you before a pitch or migration offer.
- Deliverability consultants
- Confirm which service actually sent a client's message when several are set up.
- Security teams
- Trace which service a suspicious message came through before reporting abuse to it.
What can’t this tool tell you?
- A platform set up fully on the sender's own domains may leave no recognisable trace.
- Headers can be forged above the recipient's own servers; trust the lines your provider added.
- About 40 platforms are recognised; others are listed as other DKIM signers.
Common questions
- How can I tell what ESP sent an email?
- Paste the email's raw headers here. The DKIM d= domain, Return-Path, Received servers and platform headers such as X-SG-EID name the platform, and the tool shows which lines point at it.
- Which platforms can it detect?
- Around 40 sending platforms and mailbox providers, including SendGrid, Mailchimp, Mandrill, Mailgun, Amazon SES, Postmark, SparkPost, Brevo, Mailjet, HubSpot, Klaviyo, Salesforce Marketing Cloud, Campaign Monitor, Constant Contact, Customer.io, Google and Microsoft.
- Is this ESP detector free?
- Yes. It's a free tool with no limit and no account, and it runs entirely in your browser.
- Where do I find an email's headers?
- In Gmail, open the message, click More (three dots) and Show original. In Outlook on the web, open the message's More actions, View, View message source. In Apple Mail, View, Message, All Headers.
- Can I see which ESP a company uses without one of their emails?
- Yes, from DNS: the email stack lookup reads a domain's SPF includes and DKIM records and names the platforms allowed to send as it.
Sources
Authentication and capacity are half of deliverability.
The other half is who you send to. Every hard bounce counts against the domain and inboxes you are sending from, and nothing in DNS can tell you which addresses on your list are dead.
- Bulk verification with real SMTP mailbox checks
- Hard bounces removed before a send, not discovered after
- Catch-all, disposable and role detection on every row
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