> 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/configuration/client-connection-settings.md).

# Client Connection Settings

Reference of the SMTP settings your clients use to connect to Sendman

## Server and ports

| Port  | Encryption           | Reachable from                                                                    |
| ----- | -------------------- | --------------------------------------------------------------------------------- |
| `587` | STARTTLS             | Internet and [network connections](/admin-portal/settings/network-connections.md) |
| `465` | Implicit TLS (SMTPS) | Internet and [network connections](/admin-portal/settings/network-connections.md) |
| `25`  | STARTTLS (optional)  | [Network connections](/admin-portal/settings/network-connections.md) only         |

* **Over the internet**, clients connect to `YOURNAME.sendman.com`.
* **Over a network connection**, clients connect to Sendman's tunnel address of that connection, e.g. `169.254.100.5` (see [Network Connections](/admin-portal/settings/network-connections.md#address-plan)).

{% hint style="info" %}
Whatever the port, the client's source address must be on the [IP Allow List](/admin-portal/sendman/ip-allow-list.md). Otherwise Sendman closes the connection without a reply.
{% endhint %}

## Encryption

* Sendman supports **TLS 1.2** and **TLS 1.3**, both with STARTTLS and with implicit TLS.
* Sendman's server certificate is issued for `YOURNAME.sendman.com` by a public certificate authority and is renewed automatically.
* For old devices that cannot negotiate the default cipher suites, additional TLS 1.2 cipher suites can be enabled under [SMTP Client](/admin-portal/settings/smtp-client.md).

## Authentication

| Mechanism  | Sendman credentials | Entra ID accounts |
| ---------- | :-----------------: | :---------------: |
| AUTH LOGIN |          ✅          |         ✅         |
| AUTH PLAIN |          ✅          |         ✅         |
| AUTH NTLM  |          ✅          |         ❌         |

* Clients that do not authenticate can only send if an [authorization policy](/admin-portal/sendman/authorization-policies.md#anonymous-sending) for their address range has **Allow anonymous sending** switched on.
* On ports 587 and 465, authentication is only offered and accepted after TLS is established. On port 25, it is also accepted without TLS.
* Not supported: CRAM-MD5, DIGEST-MD5, OAuth (XOAUTH2, OAUTHBEARER) and client certificate authentication.

## Limits

| Limit                            | Value                                              |
| -------------------------------- | -------------------------------------------------- |
| Maximum message size             | 25 MB (or the lower limit of your SMTP backend)    |
| Recipients per message           | Every recipient must be allowed by the same policy |
| Idle timeout                     | 2 minutes without any command                      |
| Maximum duration of a connection | 1 hour                                             |

## SMTP extensions

Sendman offers the extensions `STARTTLS`, `AUTH`, `SIZE`, `8BITMIME`, `SMTPUTF8`, `ENHANCEDSTATUSCODES` and `DSN`. The last five are only offered if your SMTP backend supports them as well. `PIPELINING` and `CHUNKING` are not offered; clients send their commands one by one.


---

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