GuideSMTP Relay

SMTP Relay Configuration

Learn how to obtain your SMTP credentials and configure your existing applications or servers to send transactional email through Simply Send.

Transactional emails only. SMTP relay is supported exclusively for transactional emails — system-triggered messages such as password resets, order confirmations, and account notifications. For marketing emails and campaigns, use the Marketing Email API instead.

Availability restrictions: SMTP relay access is enabled once your sender reputation is established. Verify your sending domain, complete your account setup, and send your first emails via the API to build a sending history before SMTP credentials become active.

1. Get Your SMTP Credentials

To start sending via SMTP, you'll need your unique SMTP credentials.

Log in to your Simply Send Dashboard.
Navigate to the SMTP on the left menu.
Create a new SMTP credentials. Keep this credentials secure.

2. Connection Settings

Use these settings in your email client, server configuration, or application code.

SMTP Host

smtp.simplysend.email

Port (STARTTLS)

587

Port (SSL/TLS)

465

Authentication

Required

3. Implementation Examples

Important note about BCC: Email libraries like Swaks and Nodemailer require a To field for the MIME message structure. When you provide a Bcc field, Simply Send will ignore the To field and send the email as BCC-only. The same applies to Cc — if both Cc and Bcc are present, only Bcc will be used.

Swaks (Bash)

Standard Email Send (To recipient visible to all)

BCC-only Send (Recipient hidden from other recipients)

Swaks requires the --to flag for the envelope recipient. When you also specify --bcc, Simply Send will use BCC for delivery and ignore the To field.

Python (smtplib)

Standard Email Send (To recipient visible to all)

BCC-only Send (Recipient hidden from other recipients, no To header in MIME)

Python's email library allows creating messages without a To header. You can use sendmail() with explicit envelope recipients for true BCC-only sends.

Node.js (Nodemailer)

Standard Email Send (To recipient visible to all)

BCC-only Send (Recipient hidden from other recipients)

Nodemailer requires a to field in the options object. When you also provide bcc, Simply Send will use BCC for delivery and ignore the To field.

4. Supported Headers

The SMTP relay extracts the following headers from your MIME message and forwards them to the API:

To — recipient email address(es)
Cc — CC recipient email address(es)
Bcc — BCC recipient email address(es). When Bcc is present, To and Cc must be omitted.
From — sender email address (must be a verified domain). Supports display name format: "Display Name" <email@example.com>
Reply-To — reply-to email address
Subject — email subject line
Attachments — MIME attachments are extracted and forwarded
Custom headers — any other headers (except standard ones like Content-Type, DKIM-Signature, etc.)

BCC-only constraint: When sending with a Bcc header, the To and Cc headers must not be present. Use either To/Cc or Bcc, not both.

Security

We support both STARTTLS on port 587 and Implicit TLS on port 465. TLS 1.2 or higher is required for all connections.

Compliance

Ensure your emails include an unsubscribe link and physical address.