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Tags are unique identifiers you can add to your emails. They help associate emails with your application. They are passed in key/value pairs. After the email is sent, the tag is included in the webhook event. Tags can include ASCII letters, numbers, underscores, or dashes. You can add up to 75 tags per email. Some examples of when to use a tag:
  • Associate the email a “customer ID” from your application
  • Add a label from your database like “free” or “enterprise”
  • Note the category of email sent, like “welcome” or “password reset”
Here’s how you can add custom tags to your emails.

​
Add tags on the POST /emails endpoint

import { Resend } from 'resend';

const resend = new Resend('re_xxxxxxxxx');

await resend.emails.send({
  from: 'Acme <onboarding@resend.dev>',
  to: ['delivered@resend.dev'],
  subject: 'hello world',
  html: '<p>it works!</p>',
  tags: [
    {
      name: 'category',
      value: 'confirm_email',
    },
  ],
});

$resend = Resend::client('re_xxxxxxxxx');

$resend->emails->send([
  'from' => 'Acme <onboarding@resend.dev>',
  'to' => ['delivered@resend.dev'],
  'subject' => 'hello world',
  'html' => '<p>it works!</p>',
  'tags' => [
    [
      'name' => 'category',
      'value' => 'confirm_email',
    ],
  ]
]);

import resend

resend.api_key = "re_xxxxxxxxx"

params: resend.Emails.SendParams = {
  "from": "Acme <onboarding@resend.dev>",
  "to": ["delivered@resend.dev"],
  "subject": "hello world",
  "html": "<p>it works!</p>",
  "tags": [
    {"name": "category", "value": "confirm_email"},
  ],
}

email = resend.Emails.send(params)
print(email)

require "resend"

Resend.api_key = "re_xxxxxxxxx"

params = {
  "from": "Acme <onboarding@resend.dev>",
  "to": ["delivered@resend.dev"],
  "subject": "hello world",
  "html": "<p>it works!</p>",
  "tags": [
    {"name": "category", "value": "confirm_email"}
  ]
}

sent = Resend::Emails.send(params)
puts sent

import (
	"fmt"

	"github.com/resend/resend-go/v3"
)

func main() {
  ctx := context.TODO()
  client := resend.NewClient("re_xxxxxxxxx")

  params := &resend.SendEmailRequest{
      From:        "Acme <onboarding@resend.dev>",
      To:          []string{"delivered@resend.dev"},
      Text:        "<p>it works!</p>",
      Subject:     "hello world",
      Tags:        []resend.Tag{{Name: "category", Value: "confirm_email"}},
  }

  sent, err := client.Emails.SendWithContext(ctx, params)

  if err != nil {
    panic(err)
  }
  fmt.Println(sent.Id)
}

use resend_rs::types::{CreateEmailBaseOptions, Tag};
use resend_rs::{Resend, Result};

#[tokio::main]
async fn main() -> Result<()> {
  let resend = Resend::new("re_xxxxxxxxx");

  let from = "Acme <onboarding@resend.dev>";
  let to = ["delivered@resend.dev"];
  let subject = "hello world";

  let email = CreateEmailBaseOptions::new(from, to, subject)
    .with_html("<p>it works!</p>")
    .with_tag(Tag::new("category", "confirm_email"));

  let _email = resend.emails.send(email).await?;

  Ok(())
}

import com.resend.*;

public class Main {
    public static void main(String[] args) {
        Resend resend = new Resend("re_xxxxxxxxx");

        Tag tag = Tag.builder()
                .name("category")
                .value("confirm_email")
                .build();

        SendEmailRequest sendEmailRequest = SendEmailRequest.builder()
                .from("Acme <onboarding@resend.dev>")
                .to("delivered@resend.dev")
                .subject("hello world")
                .html("<p>it works!</p>")
                .tags(tag)
                .build();

        SendEmailResponse data = resend.emails().send(sendEmailRequest);
    }
}

using Resend;

IResend resend = ResendClient.Create( "re_xxxxxxxxx" ); // Or from DI

var resp = await resend.EmailSendAsync( new EmailMessage()
{
    From = "Acme <onboarding@resend.dev>",
    To = "delivered@resend.dev",
    Subject = "hello world",
    HtmlBody = "<p>it works!</p>",
    ReplyTo = "onboarding@resend.dev",
    Tags = new List<EmailTag> { new EmailTag { Name = "category", Value = "confirm_email" } }
} );
Console.WriteLine( "Email Id={0}", resp.Content );

curl -X POST 'https://api.resend.com/emails' \
     -H 'Authorization: Bearer re_xxxxxxxxx' \
     -H 'Content-Type: application/json' \
     -d $'{
  "from": "Acme <onboarding@resend.dev>",
  "to": ["delivered@resend.dev"],
  "subject": "hello world",
  "html": "<p>it works!</p>",
  "tags": [
    {
      "name": "category",
      "value": "confirm_email"
    }
  ]
}'

​
Add tags on the POST /emails/batch endpoint

import { Resend } from 'resend';

const resend = new Resend('re_xxxxxxxxx');

const { data, error } = await resend.batch.send([
  {
    from: 'Acme <onboarding@resend.dev>',
    to: ['foo@gmail.com'],
    subject: 'hello world',
    html: '<h1>it works!</h1>',
    tags: [
      {
        name: 'category',
        value: 'confirm_email',
      },
    ],
  },
  {
    from: 'Acme <onboarding@resend.dev>',
    to: ['bar@outlook.com'],
    subject: 'world hello',
    html: '<p>it works!</p>',
    tags: [
      {
        name: 'category',
        value: 'confirm_email',
      },
    ],
  },
]);

$resend = Resend::client('re_xxxxxxxxx');

$resend->batch->send([
  [
    'from' => 'Acme <onboarding@resend.dev>',
    'to' => ['foo@gmail.com'],
    'subject' => 'hello world',
    'html' => '<h1>it works!</h1>',
    'tags' => [
      [
        'name' => 'category',
        'value' => 'confirm_email'
      ]
    ]
  ],
  [
    'from' => 'Acme <onboarding@resend.dev>',
    'to' => ['bar@outlook.com'],
    'subject' => 'world hello',
    'html' => '<p>it works!</p>',
    'tags' => [
      [
        'name' => 'category',
        'value' => 'confirm_email'
      ]
    ]
  ]
]);

import resend
from typing import List

resend.api_key = "re_xxxxxxxxx"

params: List[resend.Emails.SendParams] = [
  {
    "from": "Acme <onboarding@resend.dev>",
    "to": ["foo@gmail.com"],
    "subject": "hello world",
    "html": "<h1>it works!</h1>",
    "tags": [
      {
        "name": "category",
        "value": "confirm_email"
      }
    ]
  },
  {
    "from": "Acme <onboarding@resend.dev>",
    "to": ["bar@outlook.com"],
    "subject": "world hello",
    "html": "<p>it works!</p>",
    "tags": [
      {
        "name": "category",
        "value": "confirm_email"
      }
    ]
  }
]

resend.Batch.send(params)

require "resend"

Resend.api_key = 're_xxxxxxxxx'

params = [
  {
    "from": "Acme <onboarding@resend.dev>",
    "to": ["foo@gmail.com"],
    "subject": "hello world",
    "html": "<h1>it works!</h1>",
    "tags": [
      {
        "name": "category",
        "value": "confirm_email"
      }
    ]
  },
  {
    "from": "Acme <onboarding@resend.dev>",
    "to": ["bar@outlook.com"],
    "subject": "world hello",
    "html": "<p>it works!</p>",
    "tags": [
      {
        "name": "category",
        "value": "confirm_email"
      }
    ]
  }
]

Resend::Batch.send(params)

package main

import (
	"fmt"
	"os"

	"github.com/resend/resend-go/v3"
)

func main() {

  ctx := context.TODO()

  client := resend.NewClient("re_xxxxxxxxx")

  var batchEmails = []*resend.SendEmailRequest{
    {
      From:    "Acme <onboarding@resend.dev>",
      To:      []string{"foo@gmail.com"},
      Subject: "hello world",
      Html:    "<h1>it works!</h1>",
      Tags:    []resend.Tag{{Name: "category", Value: "confirm_email"}},
    },
    {
      From:    "Acme <onboarding@resend.dev>",
      To:      []string{"bar@outlook.com"},
      Subject: "world hello",
      Html:    "<p>it works!</p>",
      Tags:    []resend.Tag{{Name: "category", Value: "confirm_email"}},
    },
  }

  sent, err := client.Batch.SendWithContext(ctx, batchEmails)

  if err != nil {
    panic(err)
  }
  fmt.Println(sent.Data)
}

use resend_rs::types::CreateEmailBaseOptions;
use resend_rs::{Resend, Result};

#[tokio::main]
async fn main() -> Result<()> {
  let resend = Resend::new("re_xxxxxxxxx");

  let emails = vec![
    CreateEmailBaseOptions::new(
      "Acme <onboarding@resend.dev>",
      vec!["foo@gmail.com"],
      "hello world",
    )
    .with_html("<h1>it works!</h1>")
    .with_tag(Tag::new("category", "confirm_email")),
    CreateEmailBaseOptions::new(
      "Acme <onboarding@resend.dev>",
      vec!["bar@outlook.com"],
      "world hello",
    )
    .with_html("<p>it works!</p>")
    .with_tag(Tag::new("category", "confirm_email")),
  ];

  let _emails = resend.batch.send(emails).await?;

  Ok(())
}

import com.resend.*;

public class Main {
    public static void main(String[] args) {
        Resend resend = new Resend("re_xxxxxxxxx");

        CreateEmailOptions firstEmail = CreateEmailOptions.builder()
            .from("Acme <onboarding@resend.dev>")
            .to("foo@gmail.com")
            .subject("hello world")
            .html("<h1>it works!</h1>")
            .tags(Tag.builder()
                .name("category")
                .value("confirm_email")
                .build())
            .build();

        CreateEmailOptions secondEmail = CreateEmailOptions.builder()
            .from("Acme <onboarding@resend.dev>")
            .to("bar@outlook.com")
            .subject("world hello")
            .html("<p>it works!</p>")
            .tags(Tag.builder()
                .name("category")
                .value("confirm_email")
                .build())
            .build();

        CreateBatchEmailsResponse data = resend.batch().send(
            Arrays.asList(firstEmail, secondEmail)
        );
    }
}

using Resend;

IResend resend = ResendClient.Create( "re_xxxxxxxxx" ); // Or from DI

var mail1 = new EmailMessage()
{
    From = "Acme <onboarding@resend.dev>",
    To = "foo@gmail.com",
    Subject = "hello world",
    HtmlBody = "<p>it works!</p>",
    Tags = new List<EmailTag> { new EmailTag { Name = "category", Value = "confirm_email" } }
};

var mail2 = new EmailMessage()
{
    From = "Acme <onboarding@resend.dev>",
    To = "bar@outlook.com",
    Subject = "hello world",
    HtmlBody = "<p>it works!</p>",
    Tags = new List<EmailTag> { new EmailTag { Name = "category", Value = "confirm_email" } }
};

var resp = await resend.EmailBatchAsync( [ mail1, mail2 ] );
Console.WriteLine( "Nr Emails={0}", resp.Content.Count );

curl -X POST 'https://api.resend.com/emails/batch' \
     -H 'Authorization: Bearer re_xxxxxxxxx' \
     -H 'Content-Type: application/json' \
     -d $'[
  {
    "from": "Acme <onboarding@resend.dev>",
    "to": ["foo@gmail.com"],
    "subject": "hello world",
    "html": "<h1>it works!</h1>",
    "tags": [
      {
        "name": "category",
        "value": "confirm_email"
      }
    ]
  },
  {
    "from": "Acme <onboarding@resend.dev>",
    "to": ["bar@outlook.com"],
    "subject": "world hello",
    "html": "<p>it works!</p>",
    "tags": [
      {
        "name": "category",
        "value": "confirm_email"
      }
    ]
  }
]'