---
title: Supported SMTP headers
description: "# You can use the following SMTP headers with Inboxroad: **SMTP Headers:** - **Date:** Indicates the date and time when the message was sent. - **From:** Specifies the email address of the sender. - **To:** Specifies the email address of…"
url: "https://www.inboxroad.com/help/supported-smtp-headers/"
updated: "2026-01-08"
category: Sending Emails
---

# Supported SMTP headers

# You can use the following SMTP headers with Inboxroad:

**SMTP Headers:**

- **Date:** Indicates the date and time when the message was sent.
- **From:** Specifies the email address of the sender.
- **To:** Specifies the email address of the recipient.
- **Subject:** Contains a brief description or subject of the email.
- **Message-ID:** A unique identifier for the message.
- **In-Reply-To:** References the message to which the current message is a reply.
- **References:** Contains a list of message-ids for previous related messages.
- **Return-Path:** Specifies the email address to which bounce notifications should be sent.

**MIME Headers (Common Email Headers):**

- **Content-Type:** Describes the type of content within the email (e.g., text/plain for plain text, text/html for HTML, multipart/mixed for mixed content).
- **Content-Disposition:** Defines how the email’s content should be displayed or processed (e.g., inline or as an attachment).
- **Content-Transfer-Encoding:** Specifies how the message body is encoded (e.g., base64, quoted-printable).
- **Content-ID:** A unique identifier for inline content within the email.
- **Content-Language:** Specifies the language of the email content.
- **Content-Description:** Provides a brief description of the email’s content.
- **MIME-Version:** Indicates the MIME version used in the email (e.g., MIME-Version: 1.0).

**Additional Headers:**

- **Reply-To:** Specifies the email address to which replies should be sent, which may differ from the sender’s address.
- **CC (Carbon Copy):** Specifies email addresses of additional recipients who should receive a copy of the email.
- **BCC (Blind Carbon Copy):** Specifies email addresses of additional recipients who receive a copy of the email but are not visible to other recipients.
- **X-Headers:** Custom headers that can be added for specific purposes. These are not standardized but are sometimes used for various purposes by email clients and servers.
- Custom X headers can be added. You might need this to match the feedback to the specific emails / campaigns etc.
- We have the following custom X headers that can be used to your liking. They will only show up when they contain information.
- header_X-Job
- header_X-List
- header_X-CAMPAIGN