> For the complete documentation index, see [llms.txt](https://docs.sendman.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.sendman.com/overview.md). # Overview ## What is an SMTP relay? Many devices and applications can send e-mail but cannot talk to a modern mail service directly. Some lack support for current authentication methods, others only support outdated TLS versions, or they simply cannot be configured with the credentials of a mailbox. An **SMTP relay** sits in between: the device hands over its message using plain SMTP, and the relay delivers it to the actual mail server. Sendman provides this relay as a cloud service. Every customer gets their own Sendman instance with its own Admin Portal. ## How Sendman processes a message Every connection and every message passes through the same checks: ![](https://1641814212-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F4EVg4twS3gtObqtkynsm%2Fuploads%2Fgit-blob-19f35e4de1d11af7fbb685a1b770e5c9746ebfcc%2Fsendman-flow.svg?alt=media) 1. **IP allow list:** Sendman only accepts connections from address ranges on your [IP Allow List](/admin-portal/sendman/ip-allow-list.md). Connections from any other address are closed immediately. 2. **Authentication:** The client signs in with an [SMTP credential](/admin-portal/sendman/smtp-credentials.md) managed in Sendman, or with a Microsoft Entra ID account. If a policy allows it, clients from a defined address range may also send **anonymously**, without signing in. 3. **Authorization:** [Authorization policies](/admin-portal/sendman/authorization-policies.md) decide which sender addresses a client may use and to which recipients it may send. Without a matching policy, every message is rejected. 4. **Delivery:** Sendman forwards accepted messages to your [SMTP backend](/admin-portal/settings/smtp-backend.md), such as Exchange Online. The connection is encrypted with STARTTLS and Sendman authenticates with a username and password, a client certificate, or both. {% hint style="info" %} Changes you make in the Admin Portal apply to new connections immediately. No restart is needed. {% endhint %} ## Our Service ### Admin Portal Each customer has access to their own Sendman instance through the Sendman Admin Portal. In the portal you manage the [IP Allow List](/admin-portal/sendman/ip-allow-list.md), [Authorization Policies](/admin-portal/sendman/authorization-policies.md) and [SMTP Credentials](/admin-portal/sendman/smtp-credentials.md), configure the [SMTP backend](/admin-portal/settings/smtp-backend.md), and check the delivery of your messages in [Insights](/admin-portal/insights.md). ### Access from the internet Clients reach Sendman over the internet on the submission ports **587** (STARTTLS) and **465** (implicit TLS). TLS 1.2 and TLS 1.3 are supported. See [Client Connection Settings](/configuration/client-connection-settings.md) for all details. ### Access from your local network Optionally, you can connect your local networks to Sendman through encrypted **WireGuard** or **IPsec** tunnels (see [Network Connections](/admin-portal/settings/network-connections.md)). Clients behind such a tunnel keep their local IP address, so you can allow-list and authorize them by their internal addresses. Over a tunnel, Sendman additionally accepts mail on port **25**, which many older devices require. {% hint style="warning" %} Port 25 is never reachable from the internet. Devices that can only send on port 25 need a [network connection](/admin-portal/settings/network-connections.md). {% endhint %} ### Fixed sender IP addresses Sendman can deliver your mail through dedicated egress gateways with fixed public IP addresses. You can then restrict your mail server to accept relayed mail only from these addresses (see [Network Connections](/admin-portal/settings/network-connections.md#sendman-egress)). ## Getting Started Please follow the steps on the following page to get your first device sending mail through Sendman: {% content-ref url="/pages/kWIkOfRhI8GwbMMQdjU0" %} [Getting Started](/configuration/get-started.md) {% endcontent-ref %} --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. 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