curl --request POST \
--url https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email \
--header 'Content-Type: application/json' \
--header 'X-API-Key: <api-key>' \
--data '
{
"inbox_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"subject": "<string>",
"body_text": "<string>",
"body_html": "<string>",
"cc": [
"<string>"
],
"bcc": [
"<string>"
],
"attachments": [
{
"filename": "<string>",
"content_base64": "<string>",
"content_type": "application/octet-stream"
}
]
}
'import requests
url = "https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email"
payload = {
"inbox_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"subject": "<string>",
"body_text": "<string>",
"body_html": "<string>",
"cc": ["<string>"],
"bcc": ["<string>"],
"attachments": [
{
"filename": "<string>",
"content_base64": "<string>",
"content_type": "application/octet-stream"
}
]
}
headers = {
"X-API-Key": "<api-key>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {'X-API-Key': '<api-key>', 'Content-Type': 'application/json'},
body: JSON.stringify({
inbox_id: '3c90c3cc-0d44-4b50-8888-8dd25736052a',
subject: '<string>',
body_text: '<string>',
body_html: '<string>',
cc: ['<string>'],
bcc: ['<string>'],
attachments: [
{
filename: '<string>',
content_base64: '<string>',
content_type: 'application/octet-stream'
}
]
})
};
fetch('https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'inbox_id' => '3c90c3cc-0d44-4b50-8888-8dd25736052a',
'subject' => '<string>',
'body_text' => '<string>',
'body_html' => '<string>',
'cc' => [
'<string>'
],
'bcc' => [
'<string>'
],
'attachments' => [
[
'filename' => '<string>',
'content_base64' => '<string>',
'content_type' => 'application/octet-stream'
]
]
]),
CURLOPT_HTTPHEADER => [
"Content-Type: application/json",
"X-API-Key: <api-key>"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email"
payload := strings.NewReader("{\n \"inbox_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n \"subject\": \"<string>\",\n \"body_text\": \"<string>\",\n \"body_html\": \"<string>\",\n \"cc\": [\n \"<string>\"\n ],\n \"bcc\": [\n \"<string>\"\n ],\n \"attachments\": [\n {\n \"filename\": \"<string>\",\n \"content_base64\": \"<string>\",\n \"content_type\": \"application/octet-stream\"\n }\n ]\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("X-API-Key", "<api-key>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email")
.header("X-API-Key", "<api-key>")
.header("Content-Type", "application/json")
.body("{\n \"inbox_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n \"subject\": \"<string>\",\n \"body_text\": \"<string>\",\n \"body_html\": \"<string>\",\n \"cc\": [\n \"<string>\"\n ],\n \"bcc\": [\n \"<string>\"\n ],\n \"attachments\": [\n {\n \"filename\": \"<string>\",\n \"content_base64\": \"<string>\",\n \"content_type\": \"application/octet-stream\"\n }\n ]\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["X-API-Key"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"inbox_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n \"subject\": \"<string>\",\n \"body_text\": \"<string>\",\n \"body_html\": \"<string>\",\n \"cc\": [\n \"<string>\"\n ],\n \"bcc\": [\n \"<string>\"\n ],\n \"attachments\": [\n {\n \"filename\": \"<string>\",\n \"content_base64\": \"<string>\",\n \"content_type\": \"application/octet-stream\"\n }\n ]\n}"
response = http.request(request)
puts response.read_body{
"success": true,
"message": "<string>",
"inbox_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"inbox_email": "<string>",
"recipient_email": "<string>",
"message_id": "<string>",
"thread_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"credits_remaining": 0
}{
"detail": [
{
"loc": [
"<string>"
],
"msg": "<string>",
"type": "<string>"
}
]
}Send a direct email to a contact
Send a campaign-less 1:1 email to a contact
Compose and send a personal email straight to a contact, with no campaign behind it. The send is anchored to a campaign-less external lead so a reply threads into your inbox out-of-band — it never changes campaign status, counts or follow-ups.
Cost
Each send deducts 1 credit from the team balance. This is the only public
endpoint that spends credits, so it is also the only one that can return
402 Payment Required with {message, required, available}.
Rejections
- 409 Conflict — the contact is suppressed (blocklisted by email or
domain, unsubscribed, or bounced). Detail carries
reason,block_type,blocked_valueandemail. Nothing is charged. - 402 Payment Required — the team is out of credits. Nothing is sent.
- 404 Not Found — the contact, or the sending inbox, does not exist in this team.
- 400 Bad Request — the inbox exists but is not ACTIVE.
Choosing inbox_id
Look it up with GET /sender-accounts?status=ACTIVE and use the returned
inbox_id. Note that inbox resolution for this endpoint is team-scoped,
while GET /sender-accounts is workspace-scoped: an API key pinned to one
workspace may therefore be able to send from an inbox that the sender-accounts
list does not show. Prefer an inbox that appears in both.
Response identifiers
message_idis<direct_<lead-hex8>@domain>, the Message-ID stamped on the outbound email. Reply ingestion resolves that lead-hex on its own, which is what keeps a direct conversation separate from a campaign conversation with the same address.thread_idis the UUID of the campaign-less external thread the send — and any reply — consolidates into.- The send is queued, not awaited:
messagereadsEmail queued successfullyand delivery/bounce outcomes arrive later through webhooks.
Example Usage
import requests
contact_id = "550e8400-e29b-41d4-a716-446655440000"
response = requests.post(
f"https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email",
headers={"X-API-Key": "your-api-key"},
json={
"inbox_id": "650e8400-e29b-41d4-a716-446655440000",
"subject": "Following up on our call",
"body_text": "Hi -- wanted to send over the notes we discussed.",
}
)
print(response.json())
# {
# "success": true,
# "message": "Email queued successfully",
# "inbox_id": "650e8400-e29b-41d4-a716-446655440000",
# "inbox_email": "john@yourdomain.com",
# "recipient_email": "alice@prospect.com",
# "message_id": "<direct_1a2b3c4d@yourdomain.com>",
# "thread_id": "7a0e8400-e29b-41d4-a716-446655440000",
# "credits_remaining": 1499
# }
curl --request POST \
--url https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email \
--header 'Content-Type: application/json' \
--header 'X-API-Key: <api-key>' \
--data '
{
"inbox_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"subject": "<string>",
"body_text": "<string>",
"body_html": "<string>",
"cc": [
"<string>"
],
"bcc": [
"<string>"
],
"attachments": [
{
"filename": "<string>",
"content_base64": "<string>",
"content_type": "application/octet-stream"
}
]
}
'import requests
url = "https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email"
payload = {
"inbox_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"subject": "<string>",
"body_text": "<string>",
"body_html": "<string>",
"cc": ["<string>"],
"bcc": ["<string>"],
"attachments": [
{
"filename": "<string>",
"content_base64": "<string>",
"content_type": "application/octet-stream"
}
]
}
headers = {
"X-API-Key": "<api-key>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {'X-API-Key': '<api-key>', 'Content-Type': 'application/json'},
body: JSON.stringify({
inbox_id: '3c90c3cc-0d44-4b50-8888-8dd25736052a',
subject: '<string>',
body_text: '<string>',
body_html: '<string>',
cc: ['<string>'],
bcc: ['<string>'],
attachments: [
{
filename: '<string>',
content_base64: '<string>',
content_type: 'application/octet-stream'
}
]
})
};
fetch('https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'inbox_id' => '3c90c3cc-0d44-4b50-8888-8dd25736052a',
'subject' => '<string>',
'body_text' => '<string>',
'body_html' => '<string>',
'cc' => [
'<string>'
],
'bcc' => [
'<string>'
],
'attachments' => [
[
'filename' => '<string>',
'content_base64' => '<string>',
'content_type' => 'application/octet-stream'
]
]
]),
CURLOPT_HTTPHEADER => [
"Content-Type: application/json",
"X-API-Key: <api-key>"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email"
payload := strings.NewReader("{\n \"inbox_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n \"subject\": \"<string>\",\n \"body_text\": \"<string>\",\n \"body_html\": \"<string>\",\n \"cc\": [\n \"<string>\"\n ],\n \"bcc\": [\n \"<string>\"\n ],\n \"attachments\": [\n {\n \"filename\": \"<string>\",\n \"content_base64\": \"<string>\",\n \"content_type\": \"application/octet-stream\"\n }\n ]\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("X-API-Key", "<api-key>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email")
.header("X-API-Key", "<api-key>")
.header("Content-Type", "application/json")
.body("{\n \"inbox_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n \"subject\": \"<string>\",\n \"body_text\": \"<string>\",\n \"body_html\": \"<string>\",\n \"cc\": [\n \"<string>\"\n ],\n \"bcc\": [\n \"<string>\"\n ],\n \"attachments\": [\n {\n \"filename\": \"<string>\",\n \"content_base64\": \"<string>\",\n \"content_type\": \"application/octet-stream\"\n }\n ]\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.coldsend.pro/api/public/v1/contacts/{contact_id}/send-email")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["X-API-Key"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"inbox_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n \"subject\": \"<string>\",\n \"body_text\": \"<string>\",\n \"body_html\": \"<string>\",\n \"cc\": [\n \"<string>\"\n ],\n \"bcc\": [\n \"<string>\"\n ],\n \"attachments\": [\n {\n \"filename\": \"<string>\",\n \"content_base64\": \"<string>\",\n \"content_type\": \"application/octet-stream\"\n }\n ]\n}"
response = http.request(request)
puts response.read_body{
"success": true,
"message": "<string>",
"inbox_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"inbox_email": "<string>",
"recipient_email": "<string>",
"message_id": "<string>",
"thread_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"credits_remaining": 0
}{
"detail": [
{
"loc": [
"<string>"
],
"msg": "<string>",
"type": "<string>"
}
]
}Authorizations
API key with format cs_live_xxx
Path Parameters
Body
Compose and send a personal 1:1 email straight to a contact.
No campaign is involved: the send is anchored to a campaign-less external
lead so the reply threads into unibox out-of-band. body_text or body_html
must be provided (the service derives one from the other when only HTML is
sent). Attachments reuse the reply pipeline's base64 -> GCS path.
Team inbox to send from (must be ACTIVE)
Email subject
500Plain-text body (optional if body_html provided)
HTML body (optional if body_text provided)
CC recipients
BCC recipients
File attachments, base64-encoded. At most 5 files -- enforced here with a 422. Total size is not validated by this schema; keep it within what the sending provider accepts.
Show child attributes
Show child attributes
Response
Email accepted and queued for sending
Outcome of a direct email send.
message_id is the <direct_<leadhex>@domain> stamped on the outbound
email; thread_id is the campaign-less external thread the send (and any
reply) consolidates into. credits_remaining is the team balance after the
1-credit charge.
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