Notifications - Resend

Send email through the Resend provider adapter.

Add the adapter and notifications-core, configure the Resend API key/sender settings, and use the common email service contract. Provider acceptance of a request is distinct from delivery to the recipient mailbox.

Maven artifact	Packaging	Source project
org.fireflyframework:fireflyframework-notifications-resend	jar	modules/notifications-resend

Part of External services.

In the onboarding service

Resend is another email provider for application confirmations. Select it through its provider property, configure the API key, and register a core facade only when the application uses that service API.

Add the component

Installation and version availability explains source builds and published releases.

<dependency>
    <groupId>org.fireflyframework</groupId>
    <artifactId>fireflyframework-notifications-resend</artifactId>
    <version>26.10.20-SNAPSHOT</version>
</dependency>

Quick start

The injection examples use Lombok @RequiredArgsConstructor. Add its provided dependency and annotation processor as described in Constructor injection.

The Java examples in this section are API fragments for application code. Use the stated imports and supply the application-owned collaborators described alongside them.

If you use a core channel service instead of the provider SPI directly, register the matching service implementation explicitly. Provider auto-configuration does not expand the application's component scan.

1. Add the dependency (see Installation).

2. Select Resend and provide credentials in application.yml:

firefly:
  notifications:
    email:
      provider: resend          # selects this adapter as the active EmailProvider
    resend:
      api-key: ${RESEND_API_KEY}
      default-from: "Acme <no-reply@acme.com>"

1. Inject EmailProvider and send a message. Your code depends only on the core SPI, never on Resend:

import lombok.RequiredArgsConstructor;
import org.fireflyframework.notifications.interfaces.dtos.email.v1.EmailRequestDTO;
import org.fireflyframework.notifications.interfaces.dtos.email.v1.EmailResponseDTO;
import org.fireflyframework.notifications.interfaces.providers.email.v1.EmailProvider;
import org.springframework.stereotype.Service;
import reactor.core.publisher.Mono;

@Service
@RequiredArgsConstructor
public class WelcomeEmailService {

    private final EmailProvider emailProvider; // ResendEmailProvider, auto-wired



    public Mono<EmailResponseDTO> sendWelcome(String recipient) {
        EmailRequestDTO request = EmailRequestDTO.builder()
                .from("Acme <no-reply@acme.com>") // optional; falls back to firefly.notifications.resend.default-from
                .to(recipient)
                .subject("Welcome to Acme")
                .html("<h1>Welcome!</h1><p>Glad to have you on board.</p>")
                .text("Welcome! Glad to have you on board.")
                .build();

        return emailProvider.sendEmail(request); // -> EmailResponseDTO.success(messageId) or .error(reason)
    }
}

On success the returned EmailResponseDTO carries the Resend message id; on failure it carries the error reason (the exception is logged and swallowed, not propagated).

Configuration and wiring

The firefly.notifications.resend namespace is bound by ResendProperties.java. Nested configuration is declared in the linked class. Defaults are the field initializers.

Setting	Java type	Source default
firefly.notifications.resend.api-key	String	not initialized
firefly.notifications.resend.default-from	String	not initialized
firefly.notifications.resend.base-url	String	"https://api.resend.com"

Property-based wiring conditions found in this module:

• name = "firefly.notifications.email.provider", havingValue = "resend". ResendAutoConfiguration.java.
• prefix = "firefly.notifications.resend", name = "api-key". ResendAutoConfiguration.java.

Public API and extension points

Type	Contract and responsibility
ResendEmailProvider	Defines sendEmail, buildPayload operations.
ResendProperties	Carries apiKey, defaultFrom, baseUrl data; field constraints and defaults are declared in the linked source.
ResendAutoConfiguration	Defines resendRestClient, resendEmailProvider operations.

Related components

Related component	Why it belongs nearby
Notifications Core	Send email, SMS, and push notifications through provider ports, with templates, preferences, and metrics.
Common Client Library	Call REST, SOAP, and gRPC services through reactive client builders with shared resilience and observability facilities.

Build and test

Use Java 25. From the repository root, build this component with its required dependencies:

git clone https://github.com/fireflyframework/fireflyframework-jafly.git
cd fireflyframework-jafly
./mvnw -pl :fireflyframework-notifications-resend -am verify
./mvnw -pl :fireflyframework-notifications-resend -am install

verify runs the selected projects' tests. install makes the current build available in your local Maven repository.

This subproject has no authored src/test/java suite. Its Maven build still validates the configured compilation/generation and any reactor prerequisites. Use the consuming component tests to validate integration behavior.

API reference excerpt

Contract excerpt from ResendEmailProvider.java. This fragment needs the full type and its imports.

public class ResendEmailProvider implements EmailProvider {
    private final ResendProperties properties;
    private final RestClient resendClient;
    public Mono<EmailResponseDTO> sendEmail(EmailRequestDTO request) {
        return Mono.fromCallable(() -> buildPayload(request))
                .flatMap(payload -> resendClient
                        .post("/emails", ResendSendResponse.class)
                        .withBody(payload)
                        .execute())
                .map(resp -> EmailResponseDTO.success(resp.getId()))
                .onErrorResume(ex -> {
                    log.error("Error sending email via Resend", ex);
                    return Mono.just(EmailResponseDTO.error(ex.getMessage()));
                })
                .subscribeOn(Schedulers.boundedElastic());
    }
    private Map<String, Object> buildPayload(EmailRequestDTO req) {
        Map<String, Object> body = new LinkedHashMap<>();
        String from = StringUtils.hasText(req.getFrom()) ? req.getFrom() : properties.getDefaultFrom();
        body.put("from", from);
        body.put("to", req.getTo());
        body.put("subject", req.getSubject());
        if (StringUtils.hasText(req.getHtml())) {
            body.put("html", req.getHtml());

Detailed reference

Configuration

All properties live under the firefly.notifications.resend prefix, except the provider selector which is shared by the notifications core.

firefly:
  notifications:
    email:
      provider: resend                       # required: activates this adapter
    resend:
      api-key: ${RESEND_API_KEY}             # required: your Resend API key (re_...)
      default-from: "Acme <no-reply@acme.com>" # optional: fallback sender when a message omits `from`
      base-url: https://api.resend.com        # optional: Resend API base URL (override for tests/proxies)

Property	Default	Description
firefly.notifications.email.provider	(none)	Selector that activates this adapter. Must equal resend for the auto-configuration to apply.
firefly.notifications.resend.api-key	(none)	Resend API key used as the Bearer token. Required. the RestClient/EmailProvider beans are only created when this is present.
firefly.notifications.resend.default-from	(none)	Sender used when an EmailRequestDTO does not specify from.
firefly.notifications.resend.base-url	https://api.resend.com	Base URL of the Resend REST API. Override to point at a mock server in tests.

The auto-configuration is gated by two conditions: firefly.notifications.email.provider=resend (class-level) and the presence of firefly.notifications.resend.api-key (on the RestClient bean). If either is missing, the adapter stays inactive and another provider may take over.

How It Works

1. ResendAutoConfiguration is imported via META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports and activates when firefly.notifications.email.provider=resend.
2. It builds a named resend RestClient from ServiceClient.rest("resend") with the configured base-url, JSON content type, and an Authorization: Bearer <api-key> header.
3. It registers ResendEmailProvider as the EmailProvider bean (unless one is already defined).
4. ResendEmailProvider.sendEmail(...) translates the EmailRequestDTO into the Resend JSON payload (from, to, subject, html/text, cc, bcc, Base64 attachments) and POSTs it to /emails, mapping the response id into EmailResponseDTO.success(id).

Continue the application

Use the Notifications Core guide for the next part of this integration. The runnable submission/query service is in Getting started.

Source and further reading

• Maven project and dependency declarations.
• Production source.
• org.springframework.boot.autoconfigure.AutoConfiguration.imports.
• Module catalog and getting started.
• Maven platform and architecture.