# Schedule email

> Send an email at a future time with scheduled_at, then reschedule or cancel it before it goes out.

Pass a `scheduled_at` timestamp to `POST /emails` to hold the email and deliver it later. The value is an **ISO 8601** datetime — always send it with an explicit timezone offset (or a trailing `Z` for UTC) so there is no ambiguity about when it fires.

## Schedule a send

When `scheduled_at` is in the future, MailBlastr stores the email with status `scheduled` and enqueues an internal job that the scheduler dispatches at the requested time. Open/click tracking, custom headers, and attachments are applied at the *actual* send time, so a scheduled email is assembled identically to an immediate one.

> **Note:** Emails can be scheduled up to **30 days** in advance. A `scheduled_at` further out than that is rejected with a `validation_error`.

**Node.js**

```js
import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr('mb_xxxxxxxxx');

const { data, error } = await mb.emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": ["delivered@example.com"],
  "subject": "Your weekly digest",
  "html": "<p>Here is what you missed.</p>",
  "scheduled_at": "2026-06-24T09:00:00Z"
});
console.log({ data, error });
```

**Ruby**

```ruby
require "mailblastr"

Mailblastr.api_key = "mb_xxxxxxxxx"

Mailblastr::Emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": [
    "delivered@example.com"
  ],
  "subject": "Your weekly digest",
  "html": "<p>Here is what you missed.</p>",
  "scheduled_at": "2026-06-24T09:00:00Z"
})
```

**PHP**

```php
$mailblastr = Mailblastr::client('mb_xxxxxxxxx');

$mailblastr->emails->send([
  'from' => "Acme <hello@yourdomain.com>",
  'to' => [
    "delivered@example.com"
  ],
  'subject' => "Your weekly digest",
  'html' => "<p>Here is what you missed.</p>",
  'scheduled_at' => "2026-06-24T09:00:00Z"
]);
```

**Python**

```python
import mailblastr

mailblastr.api_key = "mb_xxxxxxxxx"

mailblastr.Emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": [
    "delivered@example.com"
  ],
  "subject": "Your weekly digest",
  "html": "<p>Here is what you missed.</p>",
  "scheduled_at": "2026-06-24T09:00:00Z"
})
```

**Go**

```go
import "github.com/shekhu10/mailblastr-sdks/mailblastr-go"

client := mailblastr.NewClient("mb_xxxxxxxxx")

params := &mailblastr.SendEmailRequest{
    From:    "Acme <hello@yourdomain.com>",
    To:      []string{"delivered@example.com"},
    Subject: "hello world",
    Html:    "<p>it works!</p>",
}
sent, err := client.Emails.Send(params)
```

**Rust**

```rust
use mailblastr::{Mailblastr, CreateEmailBaseOptions};

let mb = Mailblastr::new("mb_xxxxxxxxx");

let email = CreateEmailBaseOptions::new(
    "Acme <hello@yourdomain.com>",
    ["delivered@example.com"],
    "hello world",
).with_html("<p>it works!</p>");
let _sent = mb.emails.send(email).await?;
```

**Java**

```java
import com.mailblastr.*;

Mailblastr mailblastr = new Mailblastr("mb_xxxxxxxxx");

SendEmailRequest request = SendEmailRequest.builder()
    .from("Acme <hello@yourdomain.com>")
    .to("delivered@example.com")
    .subject("hello world")
    .html("<p>it works!</p>")
    .build();
mailblastr.emails().send(request);
```

**.NET**

```csharp
using Mailblastr;

IMailblastr mailblastr = MailblastrClient.Create("mb_xxxxxxxxx");

var resp = await mailblastr.EmailSendAsync(new EmailMessage
{
    From = "Acme <hello@yourdomain.com>",
    To = "delivered@example.com",
    Subject = "hello world",
    HtmlBody = "<p>it works!</p>",
});
```

**cURL**

```bash
curl -X POST 'https://api.mailblastr.com/emails' \
  -H 'Authorization: Bearer mb_xxxxxxxxx' \
  -H 'Content-Type: application/json' \
  -d '{
  "from": "Acme <hello@yourdomain.com>",
  "to": ["delivered@example.com"],
  "subject": "Your weekly digest",
  "html": "<p>Here is what you missed.</p>",
  "scheduled_at": "2026-06-24T09:00:00Z"
}'
```

**CLI**

```bash
mailblastr emails send \
  --from 'Acme <hello@yourdomain.com>' \
  --to 'delivered@example.com' \
  --subject 'Your weekly digest' \
  --html '<p>Here is what you missed.</p>' \
  --scheduled-at '2026-06-24T09:00:00Z'
```

> **Note:** If `scheduled_at` is in the past (or omitted), the email is sent immediately and starts as `sent` rather than `scheduled`.

## Reschedule

Change the delivery time of a still-`scheduled` email with [PATCH /emails/:id](https://www.mailblastr.com/docs/api/emails-update), passing a new `scheduled_at`. Only emails in the `scheduled` state can be rescheduled — once an email has been sent, the time is fixed.

**Node.js**

```js
import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr('mb_xxxxxxxxx');

const { data, error } = await mb.emails.update('49a3999c-0ce1-4ea6-ab68-afcd6dc2e794', { "scheduled_at": "2026-06-25T09:00:00Z" });
console.log({ data, error });
```

**Ruby**

```ruby
require "mailblastr"

Mailblastr.api_key = "mb_xxxxxxxxx"

Mailblastr::Emails.update("49a3999c-0ce1-4ea6-ab68-afcd6dc2e794", {
  "scheduled_at": "2026-06-25T09:00:00Z"
})
```

**PHP**

```php
$mailblastr = Mailblastr::client('mb_xxxxxxxxx');

$mailblastr->emails->update('49a3999c-0ce1-4ea6-ab68-afcd6dc2e794', [
  'scheduled_at' => "2026-06-25T09:00:00Z"
]);
```

**Python**

```python
import mailblastr

mailblastr.api_key = "mb_xxxxxxxxx"

mailblastr.Emails.update("49a3999c-0ce1-4ea6-ab68-afcd6dc2e794", {
  "scheduled_at": "2026-06-25T09:00:00Z"
})
```

**Go**

```go
package main

import (
    "fmt"
    "io"
    "net/http"
    "strings"
)

func main() {
    req, _ := http.NewRequest("PATCH", "https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794", strings.NewReader(`{ "scheduled_at": "2026-06-25T09:00:00Z" }`))
    req.Header.Set("Authorization", "Bearer mb_xxxxxxxxx")
    req.Header.Set("Content-Type", "application/json")
    res, _ := http.DefaultClient.Do(req)
    defer res.Body.Close()
    out, _ := io.ReadAll(res.Body)
    fmt.Println(string(out))
}
```

**Rust**

```rust
use reqwest::Client;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let res = Client::new()
        .patch("https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794")
        .header("Authorization", "Bearer mb_xxxxxxxxx")
        .header("Content-Type", "application/json")
        .body(r#"{ "scheduled_at": "2026-06-25T09:00:00Z" }"#)
        .send()
        .await?;
    println!("{}", res.text().await?);
    Ok(())
}
```

**Java**

```java
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

var client = HttpClient.newHttpClient();
var request = HttpRequest.newBuilder()
    .uri(URI.create("https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794"))
    .header("Authorization", "Bearer mb_xxxxxxxxx")
    .header("Content-Type", "application/json")
    .method("PATCH", HttpRequest.BodyPublishers.ofString("""
{ "scheduled_at": "2026-06-25T09:00:00Z" }
"""))
    .build();
var response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());
```

**.NET**

```csharp
using System.Net.Http;
using System.Text;

var client = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Patch, "https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794");
request.Headers.Add("Authorization", "Bearer mb_xxxxxxxxx");
request.Content = new StringContent(@"{ ""scheduled_at"": ""2026-06-25T09:00:00Z"" }", Encoding.UTF8, "application/json");
var response = await client.SendAsync(request);
Console.WriteLine(await response.Content.ReadAsStringAsync());
```

**cURL**

```bash
curl -X PATCH 'https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794' \
  -H 'Authorization: Bearer mb_xxxxxxxxx' \
  -H 'Content-Type: application/json' \
  -d '{ "scheduled_at": "2026-06-25T09:00:00Z" }'
```

**CLI**

```bash
mailblastr emails update 49a3999c-0ce1-4ea6-ab68-afcd6dc2e794 \
  --scheduled-at '2026-06-25T09:00:00Z'
```

## Cancel

Cancel a still-`scheduled` email with [POST /emails/:id/cancel](https://www.mailblastr.com/docs/api/emails-cancel). The email moves to `canceled` and the pending job is removed, so it will never be sent. Only `scheduled` emails can be canceled.

**Node.js**

```js
import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr('mb_xxxxxxxxx');

const { data, error } = await mb.emails.cancel('49a3999c-0ce1-4ea6-ab68-afcd6dc2e794');
console.log({ data, error });
```

**Ruby**

```ruby
require "mailblastr"

Mailblastr.api_key = "mb_xxxxxxxxx"

Mailblastr::Emails.cancel("49a3999c-0ce1-4ea6-ab68-afcd6dc2e794")
```

**PHP**

```php
$mailblastr = Mailblastr::client('mb_xxxxxxxxx');

$mailblastr->emails->cancel('49a3999c-0ce1-4ea6-ab68-afcd6dc2e794');
```

**Python**

```python
import mailblastr

mailblastr.api_key = "mb_xxxxxxxxx"

mailblastr.Emails.cancel("49a3999c-0ce1-4ea6-ab68-afcd6dc2e794")
```

**Go**

```go
package main

import (
    "fmt"
    "io"
    "net/http"
)

func main() {
    req, _ := http.NewRequest("POST", "https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794/cancel", nil)
    req.Header.Set("Authorization", "Bearer mb_xxxxxxxxx")
    res, _ := http.DefaultClient.Do(req)
    defer res.Body.Close()
    out, _ := io.ReadAll(res.Body)
    fmt.Println(string(out))
}
```

**Rust**

```rust
use reqwest::Client;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let res = Client::new()
        .post("https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794/cancel")
        .header("Authorization", "Bearer mb_xxxxxxxxx")
        .send()
        .await?;
    println!("{}", res.text().await?);
    Ok(())
}
```

**Java**

```java
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

var client = HttpClient.newHttpClient();
var request = HttpRequest.newBuilder()
    .uri(URI.create("https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794/cancel"))
    .header("Authorization", "Bearer mb_xxxxxxxxx")
    .method("POST", HttpRequest.BodyPublishers.noBody())
    .build();
var response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());
```

**.NET**

```csharp
using System.Net.Http;
using System.Text;

var client = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Post, "https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794/cancel");
request.Headers.Add("Authorization", "Bearer mb_xxxxxxxxx");
var response = await client.SendAsync(request);
Console.WriteLine(await response.Content.ReadAsStringAsync());
```

**cURL**

```bash
curl -X POST 'https://api.mailblastr.com/emails/49a3999c-0ce1-4ea6-ab68-afcd6dc2e794/cancel' \
  -H 'Authorization: Bearer mb_xxxxxxxxx'
```

**CLI**

```bash
mailblastr emails cancel 49a3999c-0ce1-4ea6-ab68-afcd6dc2e794
```

> **Warning:** Once an email is canceled it cannot be rescheduled — submit a fresh `POST /emails` to send it later.

> **Warning:** Attempting to reschedule or cancel an email that is no longer `scheduled` returns a `validation_error` — by then it has already been queued for delivery.

## Scheduled email failures

A scheduled email may still fail when its run time arrives — the dispatch is attempted later than the original request, so conditions can change in between. When this happens the email moves to `failed` and the reason is recorded on its [event log](https://www.mailblastr.com/docs/emails/managing). Common causes:

- **The API key is no longer active** — the key used to schedule the email was revoked or deleted before the run time, so MailBlastr cannot send on its behalf.
- **The recipient was suppressed in the meantime** — if every `to` recipient hard-bounced, complained, or unsubscribed between scheduling and dispatch, there is no one left to deliver to.
- **The sending domain is no longer verified** — if the `from` domain’s verification lapsed before the run time, the send is rejected.