Getting started with the transactional API

The Flexmail transactional API lets you send triggered, one-to-one emails from your application — order confirmations, password resets, invoices, and anything else that fires in response to a specific user action. You can send via HTTP (REST API) or SMTP, using the same account and credentials for both.

The transactional product works independently of the Flexmail marketing product. You can use it on its own without setting up campaigns or contact lists.

Prerequisites

• A Flexmail account. You need one to use the transactional API, even if you're only sending transactional email and not using the marketing features.
• Access to your domain's DNS settings to configure email authentication.
• Developer access to your application or sending system to integrate the API or configure SMTP.

Step 1: Activate the transactional product

If you already have a Flexmail account, activate the transactional product from the dashboard widget. The trial gives you up to 1,000 sends over 30 days at no cost. You can upgrade to a paid transactional subscription at any time during or after the trial.

If you do not have an account yet, sign up at flexmail.be/en/signup. Your marketing and transactional subscriptions are managed from the same account.

Step 2: Verify your sender address

Before you can send, you need to verify the email address you'll use in the From field.

1. Go to Settings, then Add or remove senders.
2. Add the email address you want to send from.
3. Flexmail sends a verification email to that address, click the link to confirm. This proves you own the mailbox you're sending from.

Step 3: Set up email authentication

Configure SPF, DKIM, DMARC, and a custom return-path for the domain of your sender address. These DNS records prove that your emails genuinely come from you, which is how inbox providers like Gmail decide whether to deliver your email to the inbox or reject it.

Detailed DNS configuration instructions are in the Flexmail Email API documentation , under the Email authentication section.

Step 4: Create a personal access token

The transactional API uses HTTP Basic authentication. Your account ID is the username; a personal access token is the password. These credentials are for the HTTP API only — SMTP uses separate credentials provided by Flexmail on request.

1. Go to Settings, then API, then Personal access tokens.
2. Click Create new token and give it a descriptive name.
3. Copy the token and store it securely. It won't be shown again.

Step 5: Choose your sending method

Flexmail supports two ways to send transactional email. Both use the same account ID and personal access token.

HTTP API

The REST API gives you the most control. You can send messages, manage templates, handle webhooks, and retrieve delivery data programmatically. This is the recommended approach for custom integrations and applications.

Full documentation is at email-api.flexmail.eu/documentation. The Getting started section includes a curl example you can run immediately to verify your setup.

SMTP

SMTP submissions are included in the transactional product at no extra cost. Use SMTP when your application or platform already supports it — for example, a CMS, an e-commerce platform, or a legacy system that sends email through an SMTP relay.

See "SMTP submissions for transactional email" for the connection settings and setup instructions.

Step 6: Integrate into your application

With a successful test send confirmed, you're ready to integrate the API into your application. The full documentation covers:

• Message sending: all parameters for the send endpoint
• Templates — creating and referencing reusable email templates. See "Transactional templates and personalisation" for a practical overview.
• Webhooks — real-time event notifications for sends, deliveries, bounces, opens, and clicks. See "Transactional webhooks" for setup and event reference.

API documentation and support

Full API documentation is available at email-api.flexmail.eu/documentation.

If you get stuck at any point, the Flexmail support team is available at support@flexmail.eu. Transactional API questions are handled by the same team that supports the marketing interface.

Next steps

• See 'Marketing email vs. transactional email' to understand when to use each type.
• See "SMTP submissions for transactional email" if you want to send via SMTP instead of the HTTP API.
• See "Transactional templates and personalisation" to set up reusable email templates.
• See "Transactional webhooks" to receive real-time delivery events.
• See "Transactional email troubleshooting" if something is not working as expected.
• Review the full API documentation at email-api.flexmail.eu/documentation for all endpoint parameters.