Send email with Resend through Courier

Prerequisites

A Resend account

Setup

Create a Resend API Key

In Resend, open API Keys. Create an API key and copy it.

Configure in Courier

In Courier, open the page. Paste your API key into the “API Key” field.

Set From Address

Add a verified email address to the “From Address” field (e.g., noreply@yourdomain.com). Click “Add Integration” then “Save.”

Addressing a recipient and sending are the same on every email provider, so they are documented once: and .

Overrides

covers the two levels and which one wins. lists the fields every email provider takes. A provider override changes what Courier sends to Resend’s /emails endpoint. Use one to set a field Courier does not support yet, or to replace a value Courier generates. For example, add Resend tags:

const { requestId } = await courier.send.message({
  message: {
    template: "nt_01kx4h2jdafq8bk9aftxak4b40",
    to: {
      email: "sarah@acme-corp.com",
    },
    providers: {
      resend: {
        override: {
          body: {
            tags: [
              {
                name: "environment",
                value: "development",
              },
            ],
          },
        },
      },
    },
  },
});

response = client.send.message(
    message={
        "template": "nt_01kx4h2jdafq8bk9aftxak4b40",
        "to": {
            "email": "sarah@acme-corp.com",
        },
        "providers": {
            "resend": {
                "override": {
                    "body": {
                        "tags": [
                            {
                                "name": "environment",
                                "value": "development",
                            },
                        ],
                    },
                },
            },
        },
    },
)

curl -X POST https://api.courier.com/send \
  -H "Authorization: Bearer $COURIER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "message": {
      "template": "nt_01kx4h2jdafq8bk9aftxak4b40",
      "to": {
        "email": "sarah@acme-corp.com"
      },
      "providers": {
        "resend": {
          "override": {
            "body": {
              "tags": [
                {
                  "name": "environment",
                  "value": "development"
                }
              ]
            }
          }
        }
      }
    }
  }'

response = courier.send_.message(
  message: {
    template: "nt_01kx4h2jdafq8bk9aftxak4b40",
    to: {
      email: "sarah@acme-corp.com"
    },
    providers: {
      resend: {
        override: {
          body: {
            tags: [
              {
                name: "environment",
                value: "development"
              }
            ]
          }
        }
      }
    }
  }
)

response, err := client.Send.Message(context.TODO(), courier.SendMessageParams{
	Message: courier.SendMessageParamsMessage{
		To: courier.SendMessageParamsMessageToUnion{
			OfUserRecipient: &shared.UserRecipientParam{
				Email: courier.String("sarah@acme-corp.com"),
			},
		},
		Template: courier.String("nt_01kx4h2jdafq8bk9aftxak4b40"),
		Providers: shared.MessageProvidersParam{
			"resend": shared.MessageProvidersTypeParam{
				Override: map[string]any{
					"body": map[string]any{
						"tags": []any{
							map[string]any{
								"name": "environment",
								"value": "development",
							},
						},
					},
				},
			},
		},
	},
})

SendMessageParams params = SendMessageParams.builder()
    .message(SendMessageParams.Message.builder()
        .to(UserRecipient.builder().email("sarah@acme-corp.com").build())
        .template("nt_01kx4h2jdafq8bk9aftxak4b40")
        .providers(MessageProviders.builder()
            .putAdditionalProperty("resend", JsonValue.from(java.util.Map.of("override", java.util.Map.of(
                    "body", java.util.Map.of(
                        "tags", java.util.List.of(
                            java.util.Map.of(
                                "name", "environment",
                                "value", "development"
                            )
                        )
                    )
                ))))
            .build())
        .build())
    .build();
SendMessageResponse response = client.send().message(params);

$response = $client->send->message(
  message: [
    'template' => 'nt_01kx4h2jdafq8bk9aftxak4b40',
    'to' => [
      'email' => 'sarah@acme-corp.com',
    ],
    'providers' => [
      'resend' => [
        'override' => [
          'body' => [
            'tags' => [
              [
                'name' => 'environment',
                'value' => 'development',
              ],
            ],
          ],
        ],
      ],
    ],
  ],
);

SendMessageParams parameters = new()
{
    Message = new()
    {
        To = new UserRecipient { Email = "sarah@acme-corp.com" },
        Template = "nt_01kx4h2jdafq8bk9aftxak4b40",
        Providers = new Dictionary<string, MessageProvidersType>()
        {
            {
                "resend",
                new()
                {
                    Override = JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(
                        """
                        {
                          "body": {
                            "tags": [
                              {
                                "name": "environment",
                                "value": "development"
                              }
                            ]
                          }
                        }
                        """
                    ),
                }
            },
        },
    },
};

var response = await client.Send.Message(parameters);

courier send message \
  --api-key "$COURIER_API_KEY" \
  --message.to '{"email": "sarah@acme-corp.com"}' \
  --message.template nt_01kx4h2jdafq8bk9aftxak4b40 \
  --message.providers '{"resend": {"override": {"body": {"tags": [{"name": "environment", "value": "development"}]}}}}'

With Courier MCP, send my template to sarah@acme-corp.com and set a Resend field Courier does not expose.

Courier merges everything inside message.providers.resend.override.body into its generated request body. You can also override config values:

{
  "message": {
    "providers": {
      "resend": {
        "override": {
          "config": {
            "apiKey": "<your override API key>",
            "fromAddress": "alternate-sender@yourdomain.com"
          }
        }
      }
    }
  }
}

Attachments

To include an attachment, add an attachments array in the override. File content must be base64-encoded.

const { requestId } = await courier.send.message({
  message: {
    template: "nt_01kx4h2jdafq8bk9aftxak4b40",
    to: {
      email: "sarah@acme-corp.com",
    },
    providers: {
      resend: {
        override: {
          attachments: [
            {
              filename: "billing.pdf",
              contentType: "application/pdf",
              data: "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh",
            },
          ],
        },
      },
    },
  },
});

response = client.send.message(
    message={
        "template": "nt_01kx4h2jdafq8bk9aftxak4b40",
        "to": {
            "email": "sarah@acme-corp.com",
        },
        "providers": {
            "resend": {
                "override": {
                    "attachments": [
                        {
                            "filename": "billing.pdf",
                            "contentType": "application/pdf",
                            "data": "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh",
                        },
                    ],
                },
            },
        },
    },
)

curl -X POST https://api.courier.com/send \
  -H "Authorization: Bearer $COURIER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "message": {
      "template": "nt_01kx4h2jdafq8bk9aftxak4b40",
      "to": {
        "email": "sarah@acme-corp.com"
      },
      "providers": {
        "resend": {
          "override": {
            "attachments": [
              {
                "filename": "billing.pdf",
                "contentType": "application/pdf",
                "data": "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh"
              }
            ]
          }
        }
      }
    }
  }'

response = courier.send_.message(
  message: {
    template: "nt_01kx4h2jdafq8bk9aftxak4b40",
    to: {
      email: "sarah@acme-corp.com"
    },
    providers: {
      resend: {
        override: {
          attachments: [
            {
              filename: "billing.pdf",
              contentType: "application/pdf",
              data: "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh"
            }
          ]
        }
      }
    }
  }
)

response, err := client.Send.Message(context.TODO(), courier.SendMessageParams{
	Message: courier.SendMessageParamsMessage{
		To: courier.SendMessageParamsMessageToUnion{
			OfUserRecipient: &shared.UserRecipientParam{
				Email: courier.String("sarah@acme-corp.com"),
			},
		},
		Template: courier.String("nt_01kx4h2jdafq8bk9aftxak4b40"),
		Providers: shared.MessageProvidersParam{
			"resend": shared.MessageProvidersTypeParam{
				Override: map[string]any{
					"attachments": []any{
						map[string]any{
							"filename": "billing.pdf",
							"contentType": "application/pdf",
							"data": "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh",
						},
					},
				},
			},
		},
	},
})

SendMessageParams params = SendMessageParams.builder()
    .message(SendMessageParams.Message.builder()
        .to(UserRecipient.builder().email("sarah@acme-corp.com").build())
        .template("nt_01kx4h2jdafq8bk9aftxak4b40")
        .providers(MessageProviders.builder()
            .putAdditionalProperty("resend", JsonValue.from(java.util.Map.of("override", java.util.Map.of(
                    "attachments", java.util.List.of(
                        java.util.Map.of(
                            "filename", "billing.pdf",
                            "contentType", "application/pdf",
                            "data", "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh"
                        )
                    )
                ))))
            .build())
        .build())
    .build();
SendMessageResponse response = client.send().message(params);

$response = $client->send->message(
  message: [
    'template' => 'nt_01kx4h2jdafq8bk9aftxak4b40',
    'to' => [
      'email' => 'sarah@acme-corp.com',
    ],
    'providers' => [
      'resend' => [
        'override' => [
          'attachments' => [
            [
              'filename' => 'billing.pdf',
              'contentType' => 'application/pdf',
              'data' => 'Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh',
            ],
          ],
        ],
      ],
    ],
  ],
);

SendMessageParams parameters = new()
{
    Message = new()
    {
        To = new UserRecipient { Email = "sarah@acme-corp.com" },
        Template = "nt_01kx4h2jdafq8bk9aftxak4b40",
        Providers = new Dictionary<string, MessageProvidersType>()
        {
            {
                "resend",
                new()
                {
                    Override = JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(
                        """
                        {
                          "attachments": [
                            {
                              "filename": "billing.pdf",
                              "contentType": "application/pdf",
                              "data": "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh"
                            }
                          ]
                        }
                        """
                    ),
                }
            },
        },
    },
};

var response = await client.Send.Message(parameters);

courier send message \
  --api-key "$COURIER_API_KEY" \
  --message.to '{"email": "sarah@acme-corp.com"}' \
  --message.template nt_01kx4h2jdafq8bk9aftxak4b40 \
  --message.providers '{"resend": {"override": {"attachments": [{"filename": "billing.pdf", "contentType": "application/pdf", "data": "Q29uZ3JhdHVsYXRpb25zLCB5b3UgY2FuIGJhc2U2NCBkZWNvZGUh"}]}}}'

With Courier MCP, send my template to sarah@acme-corp.com with an attachment through Resend.

Provider details

resend

Courier recommends routing to the channel. Naming this key in routing.channels instead is supported, and sends through just this provider.

Send to a specific provider

When that is worth doing, and what you give up: failover, channel priority, and providers you add later.

Get started

Available integrations

Send email with Resend through Courier

Prerequisites

Setup

Overrides

Attachments

Provider details

Send to a specific provider

​Prerequisites

​Setup

​Overrides

​Attachments

​Provider details

Send to a specific provider

Prerequisites

Setup

Overrides

Attachments

Provider details