Attachments

Attach files with the POST /send-email endpoint. They’re specified in the attachments field of the body.

This page covers the API. You can also attach files from the platform when creating a campaign: in the creation panel, under Attachments. There you upload files straight from your computer (no public URL needed) and the same types and limits below apply.

Attachment structure

Each item in the attachments array accepts these fields:

Field	Type	Required	Description
`filename`	`string`	Yes	File name with extension (e.g. `"invoice.pdf"`).
`url`	`string`	Conditional	Public URL of the file (HTTP or HTTPS). Required if `content` is not used.
`content`	`string`	Conditional	File content encoded in base64. Required if `url` is not used.
`contentType`	`string`	No	MIME type of the file. Auto-detected from the `filename` extension if not specified.

Each attachment must include filename and exactly one of url or content.

Allowed types

Only the following MIME types are allowed:

MIME type	Extension
`application/pdf`	`.pdf`
`text/calendar`	`.ics`
`audio/mpeg`	`.mp3`

If the MIME type doesn’t match these, the send fails in the background (see validation below).

Attachments cost you deliverability. On bulk sends, a binary attachment is a strong spam signal and your domain reputation pays for it. For audio or video, a button linking to your own page usually works better: lighter, plays in the browser, and tells you who opened it (an attachment doesn’t).

Limits

Limit	Value
Maximum number of attachments	10 per email
Maximum size per file	10 MB
Maximum total size	10 MB

Attachments via URL

With the url field, the server downloads the file before sending it. Security measures:

HTTP/HTTPS only: Other URL schemes are rejected.
SSRF protection: URLs pointing to private or reserved IP addresses are blocked.
Timeout: The download has a 30-second limit. If the remote server doesn’t respond in time, the send fails.

Attachments via base64

With the content field, the value must be the file encoded in base64 without prefixes (no data:...;base64,). Only the raw base64 string.

Asynchronous validation

The /send-email endpoint is asynchronous: the HTTP response confirms the email was queued, but attachments are downloaded and validated in the background. If an attachment exceeds the limits, has a disallowed MIME type, or its URL is not accessible, the send fails asynchronously and is recorded in the activity history (current_status: "failed", with the detail in error_message). To confirm the result, query the Activity API with the email_id, or subscribe to webhooks.

Examples

Attachment via URL

curl -X POST https://api.reallyquickemails.com/send-email \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk_proj_xxxxxxxxxxxx" \
  -d '{
    "recipient": "customer@example.com",
    "sender": "sales@mystore.com",
    "senderName": "My Store",
    "subject": "Your October invoice",
    "html": "<p>Attached is your October invoice.</p>",
    "attachments": [
      {
        "filename": "invoice-october-2026.pdf",
        "url": "https://storage.example.com/invoices/invoice-october-2026.pdf"
      }
    ]
  }'

Response (email queued; attachments are processed in the background):

{
  "success": true,
  "queued": true,
  "jobId": "email-1780676307345-6da66195",
  "email_id": "d116a543-9b13-41b4-93cf-647539018275",
  "activityId": "d116a543-9b13-41b4-93cf-647539018275",
  "message": "Email queued for sending"
}

Attachment via base64

curl -X POST https://api.reallyquickemails.com/send-email \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk_proj_xxxxxxxxxxxx" \
  -d '{
    "recipient": "customer@example.com",
    "sender": "sales@mystore.com",
    "senderName": "My Store",
    "subject": "Meeting invitation",
    "html": "<p>We invite you to a team meeting.</p>",
    "attachments": [
      {
        "filename": "meeting.ics",
        "content": "QkVHSU46VkNBTEVOREFSClZFUlNJT046Mi4wCkJFR0lOOlZFVkVOVApEVFNUQVJUOjIwMjUxMDE2VDE1MDAwMFoKRFRFTkQ6MjAyNTEwMTZUMTYwMDAwWgpTVU1NQVJZOlJldW5pb24gZGUgZXF1aXBvCkVORDpWRVZFTlQKRU5EOlZDQUxFTkRBUg==",
        "contentType": "text/calendar"
      }
    ]
  }'

Multiple attachments

curl -X POST https://api.reallyquickemails.com/send-email \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk_proj_xxxxxxxxxxxx" \
  -d '{
    "recipient": "customer@example.com",
    "sender": "sales@mystore.com",
    "senderName": "My Store",
    "subject": "Project documents",
    "html": "<p>Attached are the contract and the meeting agenda.</p>",
    "attachments": [
      {
        "filename": "contract.pdf",
        "url": "https://storage.example.com/docs/contract.pdf"
      },
      {
        "filename": "agenda.ics",
        "content": "QkVHSU46VkNBTEVOREFSClZFUlNJT046Mi4wCkVORDpWQ0FMRU5EQVI=",
        "contentType": "text/calendar"
      }
    ]
  }'

The response uses the same queued structure as the first example. The attachments field is not validated in the HTTP response; check the final status with the Activity API.

Guides

The app

Concepts

API Reference

Attachment structure

Allowed types

Limits

Attachments via URL

Attachments via base64

Asynchronous validation

Examples

Attachment via URL

Attachment via base64

Multiple attachments

​Attachment structure

​Allowed types

​Limits

​Attachments via URL

​Attachments via base64

​Asynchronous validation

​Examples

​Attachment via URL

​Attachment via base64

​Multiple attachments

Attachment structure

Allowed types

Limits

Attachments via URL

Attachments via base64

Asynchronous validation

Examples

Attachment via URL

Attachment via base64

Multiple attachments