Send a single email

Authorizations

Authorization

string

header

required

Sendmux API key (smx_...)

Headers

Idempotency-Key

string

Optional client-generated key to make the request idempotent for 24 hours. Replays under the same key return the cached response; a reused key with a different body returns 409 idempotency_conflict.

Maximum string length: 255

Body

application/json

from

object

required

Sender address

Hide child attributes

from.email

string<email>

required

Email address

Maximum string length: 254

Example:

"user@example.com"

from.name

string

Display name

Maximum string length: 100

Pattern: ^[^\r\n]*$

Example:

"John Smith"

object

required

Primary recipient

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to.email

string<email>

required

Email address

Maximum string length: 254

Example:

"user@example.com"

to.name

string

Display name

Maximum string length: 100

Pattern: ^[^\r\n]*$

Example:

"John Smith"

subject

string

required

Email subject line (max 998 chars, RFC 5322)

Required string length: 1 - 998

Pattern: ^[^\r\n]*$

Example:

"Welcome to Sendmux"

html_body

string

required

HTML email content (max 25MB)

Required string length: 1 - 26214400

text_body

string

Plain text alternative (max 25MB)

Maximum string length: 26214400

reply_to

object

Reply-To address

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reply_to.email

string<email>

required

Email address

Maximum string length: 254

Example:

"user@example.com"

reply_to.name

string

Display name

Maximum string length: 100

Pattern: ^[^\r\n]*$

Example:

"John Smith"

return_path

string<email>

Envelope sender for VERP support

Maximum string length: 254

object[]

CC recipients (max 100)

Maximum array length: 100

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cc.email

string<email>

required

Recipient email address

Maximum string length: 254

cc.name

string

Recipient display name

Maximum string length: 100

Pattern: ^[^\r\n]*$

bcc

object[]

BCC recipients (max 100)

Maximum array length: 100

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bcc.email

string<email>

required

Recipient email address

Maximum string length: 254

bcc.name

string

Recipient display name

Maximum string length: 100

Pattern: ^[^\r\n]*$

custom_headers

object

Custom X-* headers to include in the email

Hide child attributes

custom_headers.{key}

string

Maximum string length: 500

Pattern: ^[^\r\n]*$

attachments

object[]

File attachments (max 10)

Maximum array length: 10

Hide child attributes

attachments.filename

string

required

Filename with allowed extension

Required string length: 1 - 255

Example:

"invoice.pdf"

attachments.content

string

required

Base64-encoded file content

Minimum string length: 1

attachments.type

string

MIME type override

Example:

"application/pdf"

attachments.encoding

enum<string>

default:base64

Available options:

base64

Response

Email queued successfully

enum<boolean>

required

Available options:

true