Recently, I passed a job interview where we discussed a practical use case related to intelligent document processing and automation. In this blog series, I’ll attempt to implement key parts of that use case to evaluate how well I can design such a system and integrate the relevant tools and software.

The Use Case

We are given the following scenario:

• We use Zoho CRM/Email to ingest data — mostly in PDF format.
• We need to parse the contents of these documents.
• Finally, we aim to build an agentic AI system using RAG (Retrieval-Augmented Generation) to allow users to query the documents and automate Business Intelligence (BI) tasks.

Roadmap

Part 1 – Ingest Data (Zoho API)

Part 2 – Parse Data (LlamaIndex)

Part 3 – Build AI Agent (LangChain + RAG)

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Part 1 – Ingest Data via Zoho API

To begin, I set up a custom domain to test the Zoho integration. Authentication with the Zoho API is handled via OAuth 2.0.

Step 1: Create OAuth Credentials

I followed the guide at Zoho OAuth Request Docs and first created a Server-based Application, which provided me with a Client ID and Client Secret.

To request the authorization code:

https://accounts.zoho.eu/oauth/v2/auth?
scope=ZohoMail.messages.READ,ZohoMail.accounts.READ&
client_id=1000.xxxx&
response_type=code&
access_type=offline&
redirect_uri=https://yourdomain/oauth/callback

This redirects to:

https://yourdomain/oauth/callback?
code=1000.yyyy.zzzz&
location=eu&
accounts-server=https%3A%2F%2Faccounts.zoho.eu

Step 2: Get Access Token

Run this:

curl --request POST \
  --url "https://accounts.zoho.eu/oauth/v2/token" \
  --data "grant_type=authorization_code" \
  --data "client_id=1000.xxxx" \
  --data "client_secret=your_client_secret" \
  --data "redirect_uri=https://yourdomain/oauth/callback" \
  --data "code=1000.yyyy.zzzz"

Note: Don’t forget to replace your_client_secret with your actual client secret.

Sample Response:

{
  "access_token": "1000.ttt",
  "refresh_token": "1000.uuu",
  "scope": "ZohoMail.messages.READ ZohoMail.accounts.READ",
  "api_domain": "https://www.zohoapis.eu",
  "token_type": "Bearer",
  "expires_in": 3600
}

Step 3: Get Account ID

You need your Zoho Mail account ID to access your messages/mails:

curl --request GET \
  --url https://mail.zoho.eu/api/accounts \
  --header "Authorization: Zoho-oauthtoken 1000.ttt"

Note: This may return an error if your token scope doesn't include ZohoMail.accounts.READ.

Step 4: Fetch Emails

Once you have the account ID:

curl --request GET \
  --url "https://mail.zoho.eu/api/accounts/youraccountid/messages/view?limit=10" \
  --header "Authorization: Zoho-oauthtoken 1000.ttt"

Note: Don’t forget to replace youraccountid with your actual account id.

Example Response:

{
  "status": {
    "code": 200,
    "description": "success"
  },
  "data": [
    {
      "summary": "Hey MC, Welcome 🙏 Mahmut ÇAVDAR...",
      "subject": "Re: Test Email",
      "fromAddress": "mahmutcvdr@gmail.com",
      "hasAttachment": "0",
      "folderId":"7192274xxxx000002014",
      "messageId":"17525962xx222005600",
      ....
    }
  ]
}

If there's no attachment, "hasAttachment": "0". If there is an attachment, you can fetch its metadata:

Step 5: Get Attachment Info

Once you have the account ID:

curl "https://mail.zoho.eu/api/accounts/youraccountid/folders/7192274xxxx000002014/messages/17525962xx222005600/attachmentinfo?includeInline=true" \
-X GET \
-H "Accept: application/json" \
-H "Content-Type: application/json" \
-H "Authorization:Zoho-oauthtoken 1000.ttt"

Example Response:

{
  "status": { "code": 200, "description": "success" },
  "data": {
    "attachments": [
      {
        "attachmentName": "CV_Cavdar.pdf",
        "attachmentId": "139719xxx010000"
      }
    ]
  }
}

Step 6: Download Attachment

Once you have the account ID:

curl "https://mail.zoho.eu/api/accounts/youraccountid/folders/7192274xxxx000002014/messages/17525962xx222005600/attachments/139719xxx010000" \
-X GET \
-H "Accept: application/octet-stream" \
-H "Content-Type: application/json" \
-H "Authorization:Zoho-oauthtoken 1000.ttt" 
-o cv.pdf

And voilà — you have the attachments!

I even found an issue in the Zoho API documentation. The example on this page is incorrect — it shows the example for "Get Email Attachment Info" instead of "Get Email Attachment Content".

Wrong example:

curl "https://mail.zoho.com/api/accounts/12345678/folders/9000000002014/messages/1710915488416100001/attachmentinfo" \
-X GET \
-H "Accept: application/json" \
-H "Content-Type: application/json" \
-H "Authorization:Zoho-oauthtoken *****"

Correct Example:

curl "https://mail.zoho.com/api/accounts/12345678/folders/9000000002014/messages/1710915488416100001/attachments/139712110853010000" \
-X GET \
-H "Accept: application/octet-stream" \
-H "Content-Type: application/json" \
-H "Authorization:Zoho-oauthtoken *****"

The bug has been reported here.

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Next Steps

In Part 2, I’ll use LlamaIndex to parse PDF files and structure their contents for downstream processing. I’ll likely use this sample invoice dataset as a starting point.

In Part 3, I’ll bring in LangChain to build a agentic system that can run user queries over the ingested content and support basic BI automation tasks.