> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mailchannels.com/llms.txt
> Use this file to discover all available pages before exploring further.

# SMTP ports

> MailChannels Outbound Filtering supports connections on ports 25, 587, 2525, and 465. Use an alternative port if port 25 is blocked by your provider.

MailChannels Outbound Filtering listens on the following ports. All ports support STARTTLS encryption.

| Port   | Description                                                                                                                                                                                     |
| ------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `25`   | Standard SMTP. Preferred. Sometimes blocked by hosting providers.                                                                                                                               |
| `587`  | Standard authenticated SMTP. Requires authentication. Use this if port 25 is blocked.                                                                                                           |
| `2525` | Alternative to port 25. Commonly used on cloud platforms such as Azure that block port 25 on VMs.                                                                                               |
| `465`  | Legacy SMTP over SSL. Supported for older clients that cannot use STARTTLS. Not recommended for new configurations — see [RFC 8314](https://datatracker.ietf.org/doc/html/rfc8314#section-7.3). |

<Note>
  Port 465 was briefly registered as `smtps` but the registration was revoked and the port reassigned. MailChannels continues to support it for legacy clients only.
</Note>

If port 25 is blocked in your environment, use port **587** or **2525**. Both are configured identically to port 25.