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

# Station ID

> When the from filter finds a fax by phone, why most faxes arrive with no sender ID, and why a default ID is shared.

The `from` filter finds a fax by phone only when a sender ID reaches Faxbeep with the call. For most faxes by phone, none does.

## What the sender ID is

The ID of the machine that sends a fax is its <Tooltip headline="TSID" tip="Transmitting Subscriber Identification: the ID of the machine that sends a fax. It is usually its fax number, or a short name." cta="Glossary" href="/reference/glossary#tsid">TSID</Tooltip>, set as the station ID of the machine. It is a fax number or a short name. Faxbeep shows it as the sender of the fax, and `from` matches it. See [TSID](/reference/glossary#tsid).

The CSID is the ID of the machine that receives the fax. It is not the ID of the sender, and you cannot use it to find your fax. See [CSID](/reference/glossary#csid).

Faxbeep has no field that you can set to tag your test. The sender ID is what your machine or your fax provider sends, and Faxbeep cannot change it.

## Most faxes by phone have no sender ID

About 4 in 5 faxes by phone arrive with no sender ID. Whether it arrives depends on your machine, your fax service and the phone network, not on Faxbeep. When none arrives, faxbeep.com shows the sender as "Unknown", and the API gives `"from": null`.

| What arrives with the call | `from` in the API | Find your fax by |
| - | - | - |
| Nothing | `null` | `since` and `page_count` |
| A phone number | The number, masked | `from` with the full number |
| A station ID (a name) | The ID, as on the site | `from` with the ID, if only you use it |

A test by email always has a sender: the address in the From line. See [Find your fax](/developers/find-your-fax).

To learn what your setup sends, send one test and look at the sender on faxbeep.com. If it says "Unknown", use `since` and `page_count`. `?from=Unknown` lists the tests with no sender ID, but they are from many senders.

## How `from` matches

| Rule | Example |
| - | - |
| Full value only | `+15555550123` matches. `5550123` does not: there is no prefix and no wildcard |
| Case | `FrontDesk`, `frontdesk` and `FRONTDESK` match one sender |
| Spaces | `Front Desk` matches `FrontDesk`. The spaces of a station ID are removed |
| Plus sign | `+15555550123` and `15555550123` match the same number. Send `+` as `%2B` |
| Masked value | The masked form that the API and the site show does not find your fax |

A station ID can have 20 characters at most, and it arrives with no spaces: `Front Desk` shows as `FrontDesk`.

## A default ID is shared

<Warning>
  Many machines and fax services send a default station ID, such as `test`, `Fax` or `mFax`. Many other senders use the same ID, so `?from=test&limit=1` can give the fax of a different sender. There is no block list. Always compare `received_at` and `page_count` with what you sent, also when you filter by `from`.
</Warning>

If your machine or fax service lets you set the station ID, set one that only you use, for example a name with a random part. Then `from` finds your fax.

## Next

<Card title="Test in CI" icon="rotate" href="/developers/ci">
  A script that waits for your fax, with or without a sender ID.
</Card>


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