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SMTP

Connect an SMTP client using your existing API key.

Connection settings

Host
smtp.usesendy.com
Port
2525
Encryption
STARTTLS
Username
apikey
Password
Your full API key
Authentication
PLAIN or LOGIN after STARTTLS

Use the literal username apikey and the full key, including snd_key_, as the password. Connect with SMTP and upgrade using STARTTLS before authentication. Implicit TLS on port 465 is not supported.

For application setup, see Nodemailer, Laravel, Django, Rails, PHPMailer, or WordPress.

Want to keep using sendmail on your VPS? Configure Exim4 or Postfix to relay outbound email through Sendy. Your applications and scripts can keep their local mail submission setup, with Sendy’s SMTP credentials managed by the mail server. Sender verification still applies.

Send with curl

Save the following as email.eml. Preserve the blank line between headers and body:

email.eml
From: My App <[email protected]>
To: [email protected]
Subject: Welcome
MIME-Version: 1.0
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<h1>Welcome</h1><p>Your account is ready.</p>

SMTP submission · curl
curl --url 'smtp://smtp.usesendy.com:2525' --ssl-reqd \
  --user 'apikey:API_KEY' \
  --mail-from '[email protected]' \
  --mail-rcpt '[email protected]' \
  --upload-file email.eml

Replace API_KEY, the sender, and the recipient in both the file and command. Your account password is not used.

Message requirements

  • Use verified domains on your account for the MIME From header and any nonempty SMTP MAIL FROM. Delivery-failure notifications can use MAIL FROM:<>; the MIME From domain must still be verified. Display names belong in the MIME header.
  • The optional MAIL FROM parameter AUTH= accepts an xtext-encoded submitter address or <> for an unknown submitter. Your API key determines account access and sending permissions; AUTH= does not change them.
  • Recipients come from the SMTP envelope. To and Cc headers alone do not add recipients.
  • MIME preserves HTML, plain-text alternatives, attachments, and reply-to headers. Use your mail library to encode non-ASCII headers. Email addresses must be ASCII.
  • Provide one From header and a nonblank subject of up to 255 bytes. Sender and Resent-* headers are unsupported.
Recipients per message
Up to 50 distinct recipients.
Message size
1 MiB by default, including encoded attachments.
Line length
Up to 1,000 bytes, including its line ending.
Configured size limit
Advertised in the SMTP SIZE capability.

Retry safely with an idempotency key

Add one optional email header and reuse its value when retrying the same email:

Email header
Sendy-Idempotency-Key: welcome/user-123

Keys contain 1 to 128 printable ASCII bytes without spaces. They are case-sensitive and scoped to your account across its API keys, separately from HTTP idempotency keys. Matching retries return 250 with the original job IDs, without creating jobs or reserving credit again. Keys remain reserved while the original job records are retained; there is no time-based expiry. Without this header, each submission creates new jobs.

Keep the envelope sender, recipient set, and cleaned MIME message unchanged. Recipient order and generated Date, Message-ID, and Received headers do not affect matching. Other headers and MIME body bytes do, including multipart boundaries and attachment encoding. Preserve the composed raw message for multipart retries.

Reusing a key for a different email returns 554 5.5.0. Use a new key for new content or recipients. Empty, repeated, or malformed key headers return 554. Sendy removes the key header before delivery.

Queued response

SMTP response
250 2.0.0 Queued jobs 123,124

Sendy creates one job per recipient. This response confirms storage, not inbox delivery. Look up each returned ID with Get email status or open Emails.

Without an idempotency key, resubmitting after a lost response can create duplicate jobs. See Errors for retry guidance.