SMTP API

Our SMTP API allows you to send email transmissions directly from your own mail server (or client). It acts as an intermediary, receiving your SMTP commands, constructing a mail object, and then processing it for transmission creation.
 

Our SMTP API accepts connections on the following ports:

  • 25: Unencrypted
  • 465: SSL
  • 587: STARTTLS
 

 

Sending an Email using SMTP API

This guide outlines the steps to connect and send your first email using our SMTP API. We'll walk you through a basic SMTP transaction using the openssl s_client command-line tool for demonstration purposes.
 

For sample code in various languages like Java, Python, Node.js, and Go, check out our GitHub repository.

1. Establish a Secure Connection:

openssl s_client -connect smtp-campaigns.zoho.com:587 -starttls smtp -ign_eof -crlf

This command connects to the Zoho Campaigns server on port 587 (standard for secure SMTP) and initiates a TLS handshake using the STARTTLS extension. The -ign_eof option ensures the command doesn't terminate prematurely, and -crlf specifies using CRLF (carriage return, line feed) as the line terminator.

2. Identify Yourself:

EHLO zylker.com


Send the EHLO command followed by your domain name (zylker.com in this example). This introduces your client to the server.
 

3. Authenticate with API Key:

Use the AUTH LOGIN command to send the API key (refer to Authentication section of the API documentation here).
 

AUTH LOGIN

334 Username

YXBpa2V5 // base64 encoded value for the string "apikey"

334 Password

MTAwMC4qKioqKioqKioqKioqLioqKioqKio= // base64 encoded password

235 Continue with the mail


4. Specify the Sender:

Use the MAIL FROM command to specify the email address of the sender. Enclose the address in angle brackets < >.

MAIL FROM:<aaron@zylker.com>

250 2.1.0 Sender <aaron@zylker.com> OK

 

5. Add Recipients:

Use the RCPT TO command for each recipient address. You can add up to 10,000 recipients per email. Enclose each address in angle brackets.

RCPT TO:<aaron.test@gmail.com>

250 2.1.5 Recipient <aaron.test@gmail.com> OK

RCPT TO:<ea.test@zylker.com>

250 2.1.5 Recipient <ea.test@zylker.com> OK

 

6. Compose the Email (DATA):

  • Use the DATA command to indicate the start of the email content.
  • Provide the email subject on a separate line.
  • Add the email body content.
  • Include any optional email metadata prefixed with X-ZCEA-SMTP-DATA: (refer to API documentation for supported metadata).
  • End the email content with a single dot (.) on a new line to signal the end of the message.

 

DATA

354 Ok Send data ending with <CRLF>.<CRLF>

Subject: My first mail using Zoho Campaigns Email API SMTP

X-ZCEA-SMTP-DATA:{"campaign_name":"Summer is here","recipient_data":{"aaron.test@gmail.com":{"name":"Aaron Fletcher","additional_data":{"phone":"+91231241444","country":"CA"},"merge_data":{"first_name":"Aaron"}},"ea.test@zylker.com":{"name":"EA Test","additional_data":{"phone":"+9198762313210","country":"CA"},"merge_data":{"first_name":"EA"}}},"from":{"address":"aaron@zylker.com","name":"Aron Fletcher"}}

 

Summer Hot Savings, You Don’t Want to Miss.

7. Success:

Upon successful completion of these steps, the server will send a response indicating the email has been accepted or rejected. Refer to 'Error Codes' documentation for information on response codes.