---
title: "nextmail.labels"
description: "Every method in this namespace: its signature, its parameters, what it returns and an example."
url: "https://nextmail.sh/docs/python/reference/labels"
area: "Python"
category: "Reference"
---

# nextmail.labels

Every method in this namespace: its signature, its parameters, what it returns and an example.

## Methods

The labels a thread can carry.

### `labels.list()`

List the workspace's labels, a page at a time

```python
def list(
    *,
    limit: int | None = None,
    cursor: str | None = None,
    api_key: str | None = None,
    timeout: float | None = None,
) -> Page[LabelResource]
```

Returns one page of the workspace's user labels, sorted by name and then by id. `list_all` collects every page into one list and `iterate` walks them lazily. Each label carries its colour, `threadCount` (how many conversations carry it now) and `createdAt` and `updatedAt`, which is everything the Labels table in the app shows.

System labels such as `INBOX`, `STARRED` and `UNREAD` are not listed. A thread carries them and `threads.update` takes them, but they cannot be renamed, recoloured or deleted.

`color` is `None` on a label saved with no colour. Otherwise `color['backgroundColor']` is a hex value or a gradient token such as `gradient:sunset`, and `color['textColor']` is the ink the app draws on it, worked out on the server rather than stored.

Scopes: `labels:read`.

**Parameters**

- `limit` (`int`): Page size, from 1 to 100. The server defaults to 25.
- `cursor` (`str`): The `nextCursor` of the previous page, passed back as it came. Leave it out for the first page.
- `api_key` (`str`): Overrides the client API key for this call only.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`Page[LabelResource]`, a dict with `items`, `hasMore` and `nextCursor`. Each item has `id`, `name`, `type`, `color`, `threadCount`, `createdAt` and `updatedAt`.

**Example**

```python
from nextmail import nextmail

page = nextmail.labels.list(limit=50)

for label in page['items']:
    print(label['name'], label['threadCount'])

if page['hasMore']:
    print('more after', page['nextCursor'])
```

**Notes**

- Labels belong to the workspace, so a narrowed key still sees every label. `threadCount` is the exception: it counts only conversations delivered to the addresses the key holds.
- An id is fixed when the label is created and survives a rename, so match on `id` rather than `name` in stored configuration.
- The sidebar order in the app is each person's own arrangement and is not exposed.
- The cursor is opaque and holds where the last row sat in this order, so a row deleted or edited between pages never breaks the walk: the next page starts at the first row that sorts after it. A cursor this list did not hand out is a 400 `invalid_cursor`.

Also available in: API [`GET /labels`](https://nextmail.sh/docs/api/reference/labels#get-labels); TypeScript [`nextmail.labels.list()`](https://nextmail.sh/docs/sdk/reference/labels#list); Ruby [`labels.list`](https://nextmail.sh/docs/ruby/reference/labels#list); PHP [`labels->list`](https://nextmail.sh/docs/php/reference/labels#list); Go [`Labels.List`](https://nextmail.sh/docs/go/reference/labels#list); Java [`labels().list`](https://nextmail.sh/docs/java/reference/labels#list); C# [`Labels.ListAsync`](https://nextmail.sh/docs/csharp/reference/labels#list); CLI [`nextmail labels list`](https://nextmail.sh/docs/cli/reference/labels#labels-list).

### `labels.list_all()`

Collect every label into one list

```python
def list_all(
    *,
    limit: int | None = None,
    cursor: str | None = None,
    api_key: str | None = None,
    timeout: float | None = None,
) -> builtins.list[LabelResource]
```

Walks every page of `list` and returns all labels in one list, sorted by name and then by id. One request per page.

Scopes: `labels:read`.

**Parameters**

- `limit` (`int`): Page size for each request, from 1 to 100. The server defaults to 25.
- `cursor` (`str`): Starts the walk after this cursor instead of the first page.
- `api_key` (`str`): Overrides the client API key for every page of this walk.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`list[LabelResource]` holding every label.

**Example**

```python
from nextmail import nextmail

labels = nextmail.labels.list_all(limit=100)
ids_by_name = {label['name']: label['id'] for label in labels}

receipts = ids_by_name.get('Receipts')

if receipts is not None:
    nextmail.threads.update('thr_8f2c41d0a3b94e6f', {'addLabelIds': [receipts]})
```

**Notes**

- If any page fails, the call raises and the labels already fetched are discarded.

Also available in: API [`GET /labels`](https://nextmail.sh/docs/api/reference/labels#get-labels); TypeScript [`nextmail.labels.listAll()`](https://nextmail.sh/docs/sdk/reference/labels#listAll); Ruby [`labels.list_all`](https://nextmail.sh/docs/ruby/reference/labels#listAll); PHP [`labels->listAll`](https://nextmail.sh/docs/php/reference/labels#listAll); Go [`Labels.ListAll`](https://nextmail.sh/docs/go/reference/labels#listAll); Java [`labels().listAll`](https://nextmail.sh/docs/java/reference/labels#listAll); C# [`Labels.ListAllAsync`](https://nextmail.sh/docs/csharp/reference/labels#listAll).

### `labels.iterate()`

Stream the labels one at a time

```python
def iterate(
    *,
    limit: int | None = None,
    cursor: str | None = None,
    api_key: str | None = None,
    timeout: float | None = None,
) -> Iterator[LabelResource]
```

Returns a generator that yields labels one at a time, sorted by name and then by id, and requests the next page only once the current one is used up. Nothing is fetched until the loop starts, and breaking out of it stops the requests.

Scopes: `labels:read`.

**Parameters**

- `limit` (`int`): Page size for each request, from 1 to 100. The server defaults to 25.
- `cursor` (`str`): Starts the walk after this cursor instead of the first page.
- `api_key` (`str`): Overrides the client API key for every page of this walk.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`Iterator[LabelResource]`, a generator yielding one label per step.

**Example**

```python
from nextmail import nextmail

for label in nextmail.labels.iterate():
    if label['threadCount'] == 0:
        print('unused', label['name'])
```

**Notes**

- The generator is lazy, so an abandoned loop costs only the pages you consumed.

Also available in: API [`GET /labels`](https://nextmail.sh/docs/api/reference/labels#get-labels); TypeScript [`nextmail.labels.iterate()`](https://nextmail.sh/docs/sdk/reference/labels#iterate); Ruby [`labels.iterate`](https://nextmail.sh/docs/ruby/reference/labels#iterate); PHP [`labels->iterate`](https://nextmail.sh/docs/php/reference/labels#iterate); Go [`Labels.Iterate`](https://nextmail.sh/docs/go/reference/labels#iterate); Java [`labels().iterate`](https://nextmail.sh/docs/java/reference/labels#iterate); C# [`Labels.IterateAsync`](https://nextmail.sh/docs/csharp/reference/labels#iterate).

### `labels.list_colors()`

List the colours the app offers for labels

```python
def list_colors(
    *,
    api_key: str | None = None,
    timeout: float | None = None,
) -> builtins.list[LabelColorResource]
```

Returns the whole label palette as a plain list: the fourteen solid colours and seven gradients the app offers when you make or edit a label, in the order it shows them. It is a fixed catalogue, so there is no paging. Fetch it once and keep it.

`value` is what to send as `color['backgroundColor']`: a hex such as `#3B82F6` for a solid, a token such as `gradient:sunset` for a gradient. `textColor` is the ink drawn on it. A gradient also carries `from` and `to`, drawn at 135 degrees, and `solid`, one hex for places a gradient cannot go.

A label may carry a colour outside this list. Any hex set through the API is kept as it is, and the app offers it back as its own swatch.

Scopes: `labels:read`.

**Parameters**

- `api_key` (`str`): Overrides the client API key for this call only.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`list[LabelColorResource]`, each with `kind`, `name`, `value`, `solid`, `from`, `to` and `textColor`.

**Example**

```python
from nextmail import nextmail

colors = nextmail.labels.list_colors()
sunset = next((color for color in colors if color['name'] == 'sunset'), None)

label = nextmail.labels.create(
    {'name': 'Launch', 'color': {'backgroundColor': sunset['value'] if sunset else '#EF4444'}}
)
print(label['id'], label['color'])
```

**Notes**

- `kind` is `solid` or `gradient`. `from` and `to` are `None` on a solid.

Also available in: API [`GET /labels/colors`](https://nextmail.sh/docs/api/reference/labels#get-labels-colors); TypeScript [`nextmail.labels.listColors()`](https://nextmail.sh/docs/sdk/reference/labels#listColors); Ruby [`labels.list_colors`](https://nextmail.sh/docs/ruby/reference/labels#listColors); PHP [`labels->listColors`](https://nextmail.sh/docs/php/reference/labels#listColors); Go [`Labels.ListColors`](https://nextmail.sh/docs/go/reference/labels#listColors); Java [`labels().listColors`](https://nextmail.sh/docs/java/reference/labels#listColors); C# [`Labels.ListColorsAsync`](https://nextmail.sh/docs/csharp/reference/labels#listColors); CLI [`nextmail labels list-colors`](https://nextmail.sh/docs/cli/reference/labels#labels-list-colors).

### `labels.get()`

Read one user label by id

```python
def get(
    id: str,
    *,
    api_key: str | None = None,
    timeout: float | None = None,
) -> LabelResource
```

Looks up a single user label and returns it in the same shape as a row of `list`, with its colour, `threadCount`, `createdAt` and `updatedAt`.

Only user labels are served. `INBOX`, `TRASH` and the other system ids are a 404 here even though threads carry them. Ids are matched exactly, so `user_receipts` does not find `USER_RECEIPTS`.

Scopes: `labels:read`.

**Parameters**

- `id` (`str`, required): Label id such as `USER_RECEIPTS`, matched case sensitively.
- `api_key` (`str`): Overrides the client API key for this call only.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`LabelResource` with `id`, `name`, `type` (always `user`), `color`, `threadCount`, `createdAt` and `updatedAt`.

**Example**

```python
from nextmail import nextmail

label = nextmail.labels.get('USER_RECEIPTS')
color = label['color']

print(label['name'], color['backgroundColor'] if color else 'no colour', label['threadCount'])
```

**Notes**

- A missing label raises `NextmailApiError` with `is_not_found` set to `True` and code `resource_not_found`.

Also available in: API [`GET /labels/{id}`](https://nextmail.sh/docs/api/reference/labels#get-labels-id); TypeScript [`nextmail.labels.get()`](https://nextmail.sh/docs/sdk/reference/labels#get); Ruby [`labels.get`](https://nextmail.sh/docs/ruby/reference/labels#get); PHP [`labels->get`](https://nextmail.sh/docs/php/reference/labels#get); Go [`Labels.Get`](https://nextmail.sh/docs/go/reference/labels#get); Java [`labels().get`](https://nextmail.sh/docs/java/reference/labels#get); C# [`Labels.GetAsync`](https://nextmail.sh/docs/csharp/reference/labels#get); CLI [`nextmail labels get`](https://nextmail.sh/docs/cli/reference/labels#labels-get).

### `labels.create()`

Create a user label

```python
def create(
    body: LabelInput,
    *,
    api_key: str | None = None,
    timeout: float | None = None,
) -> LabelResource
```

Creates a label and returns it as it is stored. `name` is trimmed and must then be 1 to 225 characters. The id is derived from the name as `USER_` followed by the name upper cased, with each run of whitespace turned into `_`, so `Big Clients` becomes `USER_BIG_CLIENTS`, and it never changes afterwards.

A name another label already has, compared without case, is refused with 409 `label_name_taken`, and so is a name whose id another label holds because it was created under that name and renamed since. An existing label is never silently overwritten. A workspace holds at most 50 user labels, and the call past that is a 422 `label_limit_reached` on `name`.

`color` is optional. `color['backgroundColor']` is a hex colour (`#RGB`, `#RGBA`, `#RRGGBB` or `#RRGGBBAA`, stored upper cased) or a gradient token such as `gradient:sunset`, and anything else is a 422 `invalid_parameter` with `param` set to `color.backgroundColor`. `list_colors` returns the palette the app offers. `textColor` may be sent but is ignored: the ink is worked out from the background. Leaving `color` out stores no colour.

`aiInstructions` says what the label is for in plain words, such as `invoices and receipts`. With `aiEnabled` on, AI reads each arriving message against them and adds the label when it fits. It skips spam, the Bin, encrypted mail and muted threads, and it only labels: it never archives or moves anything. Turning `aiEnabled` on needs instructions and a paid plan, and a workspace may have 10 such labels. Without instructions it is a 422 `invalid_parameter` on `aiInstructions`, on the free plan a 403 `plan_required`, and past the tenth a 422 `ai_label_limit_reached`.

Scopes: `labels:write`.

**Parameters**

- `body['name']` (`str`, required): Display name, trimmed, 1 to 225 characters. Also decides the id.
- `body['color']` (`LabelColorInput`): The colour. Leave it out for a label with no colour.
- `body['color']['backgroundColor']` (`str`, required): A hex colour such as `#3B82F6` or a gradient token such as `gradient:sunset`, at most 32 characters. Required once `color` is given.
- `body['color']['textColor']` (`str`): Accepted and ignored. The ink is worked out from `backgroundColor`.
- `body['aiInstructions']` (`str | None`): What the label is for, in plain words, up to 500 characters, such as `invoices and receipts`.
- `body['aiEnabled']` (`bool`): Have AI apply the label to arriving mail that fits `aiInstructions`. It needs instructions and a paid plan, and a workspace may have 10 such labels.
- `api_key` (`str`): Overrides the client API key for this call only.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`LabelResource` with the new `id`, the trimmed `name`, `color`, `threadCount` of 0, `aiInstructions`, `aiEnabled`, `createdAt` and `updatedAt`.

**Example**

```python
from nextmail import nextmail

label = nextmail.labels.create(
    {'name': 'Big Clients', 'color': {'backgroundColor': 'gradient:aurora'}}
)
color = label['color']

print(label['id'], color['textColor'] if color else None)
```

**Notes**

- The SDK does not retry a create after a network failure. If you retry by hand after a lost response, a 409 `label_name_taken` means the first attempt succeeded.
- The label is created before its AI settings are saved, so a create refused with `plan_required`, `ai_label_limit_reached` or `invalid_parameter` on `aiInstructions` leaves the label in place with no instructions and `aiEnabled` off. Set them with `update` rather than creating it again.
- `test` runs the instructions over recent mail and shows what they would catch, without labelling anything.

Also available in: API [`POST /labels`](https://nextmail.sh/docs/api/reference/labels#post-labels); TypeScript [`nextmail.labels.create()`](https://nextmail.sh/docs/sdk/reference/labels#create); Ruby [`labels.create`](https://nextmail.sh/docs/ruby/reference/labels#create); PHP [`labels->create`](https://nextmail.sh/docs/php/reference/labels#create); Go [`Labels.Create`](https://nextmail.sh/docs/go/reference/labels#create); Java [`labels().create`](https://nextmail.sh/docs/java/reference/labels#create); C# [`Labels.CreateAsync`](https://nextmail.sh/docs/csharp/reference/labels#create); CLI [`nextmail labels create`](https://nextmail.sh/docs/cli/reference/labels#labels-create).

### `labels.update()`

Rename or recolour a user label

```python
def update(
    id: str,
    patch: LabelPatch,
    *,
    api_key: str | None = None,
    timeout: float | None = None,
) -> LabelResource
```

Renames a label, recolours it, or changes what AI does with it, and returns it as it is stored. Send any of `name`, `color`, `aiInstructions` and `aiEnabled`: a key left out stays as it is, and a patch with none of them is a 422. `{'color': None}`, or an empty `backgroundColor`, clears the colour.

The id never changes. A label created as `Receipts` keeps `USER_RECEIPTS` after a rename to `Invoices`, and every thread keeps the label. A new name another label already has, compared without case, is refused with 409 `label_name_taken`.

Colours follow the rules on `create`: a hex value or a gradient token, and anything else is a 422 `invalid_parameter`. Only user labels can be changed, and a system label id is a 404.

With `aiEnabled` on, AI reads each arriving message against `aiInstructions` and adds the label when it fits. It skips spam, the Bin, encrypted mail and muted threads, and it only labels: it never archives or moves anything. Turning it on needs instructions and a paid plan, and a workspace may have 10 such labels. Without instructions it is a 422 `invalid_parameter` on `aiInstructions`, on the free plan a 403 `plan_required`, and past the tenth a 422 `ai_label_limit_reached`. `{'aiInstructions': None}` clears the instructions, which also turns `aiEnabled` off.

Scopes: `labels:write`.

**Parameters**

- `id` (`str`, required): Label id such as `USER_RECEIPTS`.
- `patch['name']` (`str`): New display name, trimmed, 1 to 225 characters. Left out, the name stays.
- `patch['color']` (`LabelColorInput | None`): New colour. `None` clears it, and leaving it out keeps the stored colour.
- `patch['color']['backgroundColor']` (`str`, required): A hex colour or a gradient token, at most 32 characters. An empty string clears the colour.
- `patch['color']['textColor']` (`str`): Accepted and ignored. The ink is worked out from `backgroundColor`.
- `patch['aiInstructions']` (`str | None`): What the label is for, in plain words, up to 500 characters. `None` clears it, which also turns `aiEnabled` off. Left out, it stays.
- `patch['aiEnabled']` (`bool`): Whether AI applies the label to arriving mail that fits `aiInstructions`. Turning it on needs instructions and a paid plan, and a workspace may have 10 such labels. Left out, it stays.
- `api_key` (`str`): Overrides the client API key for this call only.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`LabelResource` with the unchanged `id` and the new `name`, `color`, `aiInstructions` and `aiEnabled`.

**Example**

```python
from nextmail import nextmail

saved = nextmail.labels.update('USER_RECEIPTS', {'color': {'backgroundColor': '#EA9602'}})
color = saved['color']

print(saved['id'], saved['name'], color['backgroundColor'] if color else None)
```

**Notes**

- The SDK retries this call after a network failure, since the same patch sent twice leaves the same label.
- `test` runs instructions over recent mail and shows what they would catch, so you can try wording before you save it here.

Also available in: API [`PATCH /labels/{id}`](https://nextmail.sh/docs/api/reference/labels#patch-labels-id); TypeScript [`nextmail.labels.update()`](https://nextmail.sh/docs/sdk/reference/labels#update); Ruby [`labels.update`](https://nextmail.sh/docs/ruby/reference/labels#update); PHP [`labels->update`](https://nextmail.sh/docs/php/reference/labels#update); Go [`Labels.Update`](https://nextmail.sh/docs/go/reference/labels#update); Java [`labels().update`](https://nextmail.sh/docs/java/reference/labels#update); C# [`Labels.UpdateAsync`](https://nextmail.sh/docs/csharp/reference/labels#update); CLI [`nextmail labels update`](https://nextmail.sh/docs/cli/reference/labels#labels-update).

### `labels.test()`

Try a label on recent mail

```python
def test(
    id: str,
    body: LabelTest | None = None,
    *,
    api_key: str | None = None,
    timeout: float | None = None,
) -> LabelTestResource
```

Runs the AI over the newest 20 inbox threads and returns the ones the label would catch, without labelling anything. Send `aiInstructions` to try wording you have not saved yet, or leave `body` out to try what the label holds.

It spends one AI action of the caller, which the labelling of arriving mail never does. A message that arrived encrypted is skipped, and a key limited to particular addresses reads only the threads delivered to them.

Scopes: `labels:write`, `threads:read`.

**Parameters**

- `id` (`str`, required): Label id such as `USER_RECEIPTS`, as `list` returns it.
- `body['aiInstructions']` (`str`): What the label is for, in plain words, 1 to 500 characters. Left out, the instructions saved on the label are tried.
- `api_key` (`str`): Overrides the client API key for this call only.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`LabelTestResource` with `object` set to `label_test`, `labelId`, `examined` and `matched`. `examined` is how many recent threads were read, and each match has `threadId`, `subject`, `sender` and `receivedOn`, with `sender` the address the newest message is from and `receivedOn` when it arrived, as its Date header gives it, or `None`.

**Example**

```python
from nextmail import nextmail

result = nextmail.labels.test('USER_RECEIPTS', {'aiInstructions': 'invoices and receipts'})

print(f'{len(result["matched"])} of {result["examined"]} would get the label')

for match in result['matched']:
    print(match['sender'], match['subject'])
```

**Notes**

- Needs both `labels:write` and `threads:read`. An unknown label id is a 404.
- With no instructions to try, neither in the call nor on the label, it is a 422 `invalid_parameter`. A spent AI allowance is a 429 `ai_quota_exceeded`, and a 409 `ai_not_configured` while AI is unavailable.
- Nothing is saved: the label keeps the instructions it had. Save the wording with `update` once it catches what you want.
- The SDK does not retry it, because each call spends an AI action.

Also available in: API [`POST /labels/{id}/test`](https://nextmail.sh/docs/api/reference/labels#post-labels-id-test); TypeScript [`nextmail.labels.test()`](https://nextmail.sh/docs/sdk/reference/labels#test); Ruby [`labels.test`](https://nextmail.sh/docs/ruby/reference/labels#test); PHP [`labels->test`](https://nextmail.sh/docs/php/reference/labels#test); Go [`Labels.Test`](https://nextmail.sh/docs/go/reference/labels#test); Java [`labels().test`](https://nextmail.sh/docs/java/reference/labels#test); C# [`Labels.TestAsync`](https://nextmail.sh/docs/csharp/reference/labels#test); CLI [`nextmail labels test`](https://nextmail.sh/docs/cli/reference/labels#labels-test).

### `labels.delete()`

Delete a user label and remove it from every thread

```python
def delete(
    id: str,
    *,
    api_key: str | None = None,
    timeout: float | None = None,
) -> DeletedLabelResource
```

Deletes a user label and, in the same transaction, takes it off every thread that carried it. The threads are otherwise untouched, so a thread that was only filed under this label stays in whatever folder it was in.

There is no undo. Creating a label with the same name again produces the same id, but the threads it was removed from do not get it back. Only user labels can be deleted, and a system label id is a 404.

Scopes: `labels:write`.

**Parameters**

- `id` (`str`, required): Label id such as `USER_OLD_PROJECT`.
- `api_key` (`str`): Overrides the client API key for this call only.
- `timeout` (`float`): Seconds this call may take, the response included, before it raises `NextmailNetworkError` with `is_timeout`. It overrides the client's `timeout` for this call, and `0` turns the limit off.

**Returns**

`DeletedLabelResource` with `object` set to `label`, the `id`, and `deleted` set to `True`.

**Example**

```python
from nextmail import nextmail

removed = nextmail.labels.delete('USER_OLD_PROJECT')

print(removed['id'], removed['deleted'])
```

**Notes**

- The SDK does not retry a delete. A 404 on your own second attempt after a lost response means the first one worked.
- `get` first if you want to say how many conversations will lose the label: its `threadCount` is that number.

Also available in: API [`DELETE /labels/{id}`](https://nextmail.sh/docs/api/reference/labels#delete-labels-id); TypeScript [`nextmail.labels.delete()`](https://nextmail.sh/docs/sdk/reference/labels#delete); Ruby [`labels.delete`](https://nextmail.sh/docs/ruby/reference/labels#delete); PHP [`labels->delete`](https://nextmail.sh/docs/php/reference/labels#delete); Go [`Labels.Delete`](https://nextmail.sh/docs/go/reference/labels#delete); Java [`labels().delete`](https://nextmail.sh/docs/java/reference/labels#delete); C# [`Labels.DeleteAsync`](https://nextmail.sh/docs/csharp/reference/labels#delete); CLI [`nextmail labels delete`](https://nextmail.sh/docs/cli/reference/labels#labels-delete).