---
title: "Which service sent it"
description: "The mail service a message was sent with, beside the sender, and a note when it reached you through a forward."
url: "https://openemail.uk/docs/knowledge/safety/sent-with"
area: "Knowledge base"
category: "Safety & authenticity"
status: "live"
---

# Which service sent it

The mail service a message was sent with, beside the sender, and a note when it reached you through a forward.

## Details

- Beside the sender, a mark names the service the message was sent with: Gmail, Outlook, iCloud Mail, Yahoo Mail, Proton Mail, Zoho Mail, Fastmail, Resend, SendGrid, Mailgun, Postmark, Mailchimp, Brevo, SparkPost, HubSpot, Amazon SES or OpenEmail. Details lists it too, as Sent with.
- It is read from the headers as the message arrives: the signing key, the service’s own headers, the domain in the Message-ID and the mail program it names, in that order. Mail from a domain that sends through OpenEmail shows as OpenEmail, and so does everything you send. On mail stored before this existed only the Message-ID is read, which can name the large providers but never Resend, Mailgun, Postmark, HubSpot or OpenEmail.
- Mail that reached you through a forward says so: a Forwarded badge by the To line, and a note above the message, Forwarded from that address, explaining that you cannot reply from it. Mail addressed to nobody you own, such as a copy passed on to you, says Sent to that address instead. Replies always go out from one of your own addresses.
- Both are read from headers the sender writes, so they describe a message rather than prove where it came from; the sender checks under Details are the part that can be trusted. A Bcc leaves no trace, so it is never shown as a forward.
- The REST API and the SDK return the service as sentWith and the forward as forwardedFrom on every message, and the MCP server includes both for the latest message of a conversation.