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Embed Inline Images

You can optionally embed an image in the HTML body of the email. This allows you to include images without needing to host them in an external server.

  1. Add the CID in the email HTML.

    Use the prefix cid: to reference the ID in the src attribute of an image tag in the HTML body of the email.

    HTML
      <img src="cid:logo-image">

  2. Reference the CID in the attachment.

    Include the content id parameter in the attachment object (see below for example implementations). The ID is an arbitrary string set by you, and must be less than 128 characters.

Implementation details

Section titled “Implementation details”

Both remote and local attachments are supported. All attachment requirements, options, and limitations apply to inline images as well.

As with all our features, inline images are available across all our SDKs.

Remote image example

Section titled “Remote image example”
Node.js
import { Resend } from 'resend';

const resend = new Resend('re_xxxxxxxxx');

await resend.emails.send({
  from: 'Acme <onboarding@resend.dev>',
  to: ['delivered@resend.dev'],
  subject: 'Thank you for contacting us',
  html: '<p>Here is our <img src="cid:logo-image"/> inline logo</p>',
  attachments: [
    {
      path: 'https://resend.com/static/sample/logo.png',
      filename: 'logo.png',
      contentId: 'logo-image',
    },
  ],
});
PHP
$resend = Resend::client('re_xxxxxxxxx');$resend->emails->send([  'from' => 'Acme <onboarding@resend.dev>',  'to' => ['delivered@resend.dev'],  'subject' => 'Thank you for contacting us',  'html' => '<p>Here is our <img src="cid:logo-image"/> inline logo</p>',  'attachments' => [    [      'path' => 'https://resend.com/static/sample/logo.png',      'filename' => 'logo.png',      'content_id' => 'logo-image',    ]  ]]);
Python
import resendresend.api_key = "re_xxxxxxxxx"attachment: resend.RemoteAttachment = {  "path": "https://resend.com/static/sample/logo.png",  "filename": "logo.png",  "content_id": "logo-image",}params: resend.Emails.SendParams = {  "from": "Acme <onboarding@resend.dev>",  "to": ["delivered@resend.dev"],  "subject": "Thank you for contacting us",  "html": "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",  "attachments": [attachment],}resend.Emails.send(params)
Ruby
require "resend"

Resend.api_key = "re_xxxxxxxxx"

params = {
  "from": "Acme <onboarding@resend.dev>",
  "to": ["delivered@resend.dev"],
  "subject": "Thank you for contacting us",
  "html": "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",
  "attachments": [
    {
      "path": "https://resend.com/static/sample/logo.png",
      "filename": 'logo.png',
      "content_id": "logo-image",
    }
  ]
}

Resend::Emails.send(params)
Go
package main

import (
	"context"
	"fmt"

	"github.com/resend/resend-go/v4"
)

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

  attachment := &resend.Attachment{
    Path:  "https://resend.com/static/sample/logo.png",
    Filename: "logo.png",
    ContentId: "logo-image",
  }

  params := &resend.SendEmailRequest{
      From:        "Acme <onboarding@resend.dev>",
      To:          []string{"delivered@resend.dev"},
      Subject:     "Thank you for contacting us",
      Html:        "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",
      Attachments: []*resend.Attachment{attachment},
  }

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

  if err != nil {
    panic(err)
  }
  fmt.Println(sent.Id)
}
Rust
use resend_rs::types::{CreateAttachment, CreateEmailBaseOptions};
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 = "Thank you for contacting us";

  let path = "https://resend.com/static/sample/logo.png";
  let filename = "logo.png";
  let content_id = "logo-image";

  let email = CreateEmailBaseOptions::new(from, to, subject)
    .with_html("<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>")
    .with_attachment(
      CreateAttachment::from_path(path)
        .with_filename(filename)
        .with_content_id(content_id),
    );

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

  Ok(())
}
Java
import com.resend.*;
import com.resend.core.exception.ResendException;
import com.resend.services.emails.model.Attachment;
import com.resend.services.emails.model.CreateEmailOptions;
import com.resend.services.emails.model.CreateEmailResponse;

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

        Attachment att = Attachment.builder()
                .path("https://resend.com/static/sample/logo.png")
                .fileName("logo.png")
                .contentId("logo-image")
                .build();

        CreateEmailOptions params = CreateEmailOptions.builder()
                .from("Acme <onboarding@resend.dev>")
                .to("delivered@resend.dev")
                .subject("Thank you for contacting us")
                .html("<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>")
                .attachments(att)
                .build();

        CreateEmailResponse data = resend.emails().send(params);
    }
}
.NET
using Resend;
using System.Collections.Generic;

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

var message = new EmailMessage()
{
    From = "Acme <onboarding@resend.dev>",
    To = "delivered@resend.dev",
    Subject = "Thank you for contacting us",
    HtmlBody = "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",
};

message.Attachments = new List<EmailAttachment>();
message.Attachments.Add( new EmailAttachment() {
  Filename = "logo.png",
  Path = "https://resend.com/static/sample/logo.png",
  ContentId = "logo-image",
} );

var resp = await resend.EmailSendAsync( message );
Console.WriteLine( "Email Id={0}", resp.Content );
cURL
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": "Thank you for contacting us",  "html": "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",  "attachments": [    {      "path": "https://resend.com/static/sample/logo.png",      "filename": "logo.png",      "content_id": "logo-image"    }  ]}'

Local image example

Section titled “Local image example”
Node.js
import { Resend } from 'resend';
import fs from 'fs';

const resend = new Resend('re_xxxxxxxxx');

const filepath = `${__dirname}/static/logo.png`;
const attachment = fs.readFileSync(filepath).toString('base64');

await resend.emails.send({
  from: 'Acme <onboarding@resend.dev>',
  to: ['delivered@resend.dev'],
  subject: 'Thank you for contacting us',
  html: '<p>Here is our <img src="cid:logo-image"/> inline logo</p>',
  attachments: [
    {
      content: attachment,
      filename: 'logo.png',
      contentId: 'logo-image',
    },
  ],
});
PHP
$resend = Resend::client('re_xxxxxxxxx');

$attachment = base64_encode(file_get_contents(__DIR__ . '/static/logo.png'));

$resend->emails->send([
  'from' => 'Acme <onboarding@resend.dev>',
  'to' => ['delivered@resend.dev'],
  'subject' => 'Thank you for contacting us',
  'html' => '<p>Here is our <img src="cid:logo-image"/> inline logo</p>',
  'attachments' => [
    [
      'filename' => 'logo.png',
      'content' => $attachment,
      'content_id' => 'logo-image',
    ]
  ]
]);
Python
import os
import resend

resend.api_key = "re_xxxxxxxxx"

f: bytes = open(
  os.path.join(os.path.dirname(__file__), "../static/logo.png"), "rb"
).read()

attachment: resend.Attachment = {"content": list(f), "filename": "logo.png", "content_id": "logo-image"}

params: resend.Emails.SendParams = {
  "from": "Acme <onboarding@resend.dev>",
  "to": ["delivered@resend.dev"],
  "subject": "Thank you for contacting us",
  "html": "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",
  "attachments": [attachment],
}

resend.Emails.send(params)
Ruby
require "resend"Resend.api_key = "re_xxxxxxxxx"file = IO.read("logo.png")params = {  "from": "Acme <onboarding@resend.dev>",  "to": ["delivered@resend.dev"],  "subject": "Thank you for contacting us",  "html": "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",  "attachments": [    {      "content": file.bytes,      "filename": 'logo.png',      "content_id": "logo-image",    }  ]}Resend::Emails.send(params)
Go
package main

import (
	"context"
	"fmt"
	"os"

	"github.com/resend/resend-go/v4"
)

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

  pwd, _ := os.Getwd()
  f, err := os.ReadFile(pwd + "/static/logo.png")
  if err != nil {
    panic(err)
  }

  attachment := &resend.Attachment{
    Content:  f,
    Filename: "logo.png",
    ContentId: "logo-image",
  }

  params := &resend.SendEmailRequest{
      From:        "Acme <onboarding@resend.dev>",
      To:          []string{"delivered@resend.dev"},
      Subject:     "Thank you for contacting us",
      Html:        "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",
      Attachments: []*resend.Attachment{attachment},
  }

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

  if err != nil {
    panic(err)
  }
  fmt.Println(sent.Id)
}
Rust
use std::fs::File;use std::io::Read;use resend_rs::types::{CreateAttachment, CreateEmailBaseOptions};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 = "Thank you for contacting us";  let filename = "logo.png";  let content_id = "logo-image";  let mut f = File::open(filename).unwrap();  let mut invoice = Vec::new();  f.read_to_end(&mut invoice).unwrap();  let email = CreateEmailBaseOptions::new(from, to, subject)    .with_html("<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>")    .with_attachment(      CreateAttachment::from_content(invoice)        .with_filename(filename)        .with_content_id(content_id),    );  let _email = resend.emails.send(email).await?;  Ok(())}
Java
import com.resend.*;
import com.resend.core.exception.ResendException;
import com.resend.services.emails.model.Attachment;
import com.resend.services.emails.model.CreateEmailOptions;
import com.resend.services.emails.model.CreateEmailResponse;

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

        Attachment att = Attachment.builder()
                .fileName("logo.png")
                .content("invoiceBuffer")
                .contentId("logo-image")
                .build();

        CreateEmailOptions params = CreateEmailOptions.builder()
                .from("Acme <onboarding@resend.dev>")
                .to("delivered@resend.dev")
                .subject("Thank you for contacting us")
                .html("<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>")
                .attachments(att)
                .build();

        CreateEmailResponse data = resend.emails().send(params);
    }
}
.NET
using Resend;
using System.Collections.Generic;
using System.IO;

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

var message = new EmailMessage()
{
    From = "Acme <onboarding@resend.dev>",
    To = "delivered@resend.dev",
    Subject = "Thank you for contacting us",
    HtmlBody = "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",
};

message.Attachments = new List<EmailAttachment>();
message.Attachments.Add( new EmailAttachment() {
  Filename = "logo.png",
  Content = await File.ReadAllBytesAsync( "logo.png" ),
  ContentId = "logo-image",
} );

var resp = await resend.EmailSendAsync( message );
Console.WriteLine( "Email Id={0}", resp.Content );
cURL
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": "Thank you for contacting us",
  "html": "<p>Here is our <img src=\"cid:logo-image\"/> inline logo</p>",
  "attachments": [
    {
      "content": "UmVzZW5kIGF0dGFjaG1lbnQgZXhhbXBsZS4gTmljZSBqb2Igc2VuZGluZyB0aGUgZW1haWwh%",
      "filename": "invoice.txt",
      "content_id": "logo-image"
    }
  ]
}'

Other considerations

Section titled “Other considerations”

Before adding inline images, consider the following.

  • As these images are sent as attachments, you need to encode your image as Base64 when sending the raw content via the API. There is no need to do this when passing the path of a remote image (the API handles this for you).
  • Inline images increase the size of the email.
  • Inline images may be rejected by some clients (especially webmail).
  • As with all attachments, add a content_type (e.g. image/png) or filename (e.g. logo.png) parameter to the attachment object. This helps email clients render the attachment correctly.
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