What you’ll learn in this guide

How to:

build a mini AI agent to classify lead replies either as positive or negative
detect such replies and classify them automatically with your agent
mark leads as interested or not in lemlist automatically to refresh your campaign stats
manufacture highly customized and SDR-friendly notifications in Slack
warn your SDRs in Slack within 2 minutes of positive replies with such notifications

Imagine…

Outbound is front and center in your acquisition; you have tens of hyper-segmented campaigns running all year round on lemlist; and you’ve been going at it for years. So much so, that you get a few tens of replies to your emails every day. Unfortunately, by waiting for SDRs to log into lemlist and check for replies, leads have already had time to cool down 10 times.

Your conversion rates are not as high as they should be.

The faster SDRs reply to interested leads, the higher their chances of converting them. Which is why they need to know about positive replies as soon as possible. If only there was a way to:

automatically categorize lead replies
and warn SDRs no later than 2 minutes after someone interested replied…

Warn SDRs in Slack when a lead seems interested

Overview: connect lemlist to Slack with OpenAI and n8n

Why Slack?

Well, that’s the one place where you can find SDRs throughout the day. So if there’s a place to warn them about interested leads, this is the one.

Why OpenAI?

Deducing from an email (natural language) whether someone is interested about something is EXACTLY what LLMs (large language models) are good at. Also, OpenAI has a lot of APIs to enable automation use cases like ours. (but to be fair, there are plenty LLM options to choose from — not only OpenAI)

Why n8n?

We need to:

automatically read a lead’s response to our campaign, with minimal latency
automatically send the text of that email to OpenAI and have it reply with true or false depending on whether the lead is interested or not
from the answer, we must automatically:
- mark the lead as interested or not interested in lemlist (to automatically refresh campaign analytics)
- automatically send a slack notification when a lead is interested

So yeah, we need to automate. Hence n8n — my favorite automation tool. So, without further ado, let’s build!

Detect lead replies in lemlist instantaneously with n8n

Head over to n8n and create a new workflow
Search through the list of lemlist triggers for “On emails replied”, add it to your wf and make sure that the isFirst parameter is set to true (otherwise, the workflow will get triggered multiple times if you send emails back and forth with a lead).
adding on emails replied trigger in n8n
Now your workflow will start each time a lead replies by email to your campaigns, with the content of their reply as input. Exactly what we wanted!
Activate your workflow and activate the option to save production executions
activating workflow and saving production executions

We still need some input data to develop the rest of our workflow, which is why i had you activate the workflow and save production executions at step 3. Now, you can either:

wait for a lead to actually reply to one of your campaigns (could be long)
create a test campaign, send an email to yourself and reply to it like a lead would
or just use the sample data below and use it as mock data in your node

sample data

[
    {
    "_id": "act_9kwPs4aQkehRNx878",
    "type": "emailsReplied",
    "emailId": "eml_txgGWZj3keB6z9Wew",
    "messageId": "<CADhdMOY2ovqWh-Wc7XvuDttkOTL=T9ZfTMR9AA-ZtKSXmQqn8Q@mail.gmail.com>",
    "createdBy": "usr_AzyCDxe92WNSrGkPz",
    "createdAt": "2025-11-18T23:11:26.000Z",
    "fromEmail": "[email protected]",
    "isFirst": true,
    "stopped": true,
    "subject": "Re: revops opportunity",
    "messagePreview": "Hey Lucas, i’ve heard only good things about lemlist, let’s talk! Here’s my",
    "bot": false,
    "teamId": "tea_b4rMsi2trB42WyuWP",
    "leadId": "lea_o3uCcHsibhy9id8qD",
    "campaignId": "cam_eMZnxqs9Z9nqGxzwT",
    "sequenceId": "seq_GPRQmr4Y5iTi4WYwL",
    "sequenceStep": 0,
    "emailTemplateId": "etp_6PNqhHqZyXeAydJyb",
    "sendUserId": "usr_AzyCDxe92WNSrGkPz",
    "totalSequenceStep": 0,
    "name": "NEW TO DELETE",
    "sendUserName": "Lucille Rabaux",
    "sendUserEmail": "[email protected]",
    "sendUserMailboxId": "usm_JLtj28DpEdrwseTAc",
    "sendUserMailboxProviderId": "[email protected]",
    "leadEmail": "[email protected]",
    "contactId": "ctc_ARyApP88xS286tgsY",
    "relatedSentAt": "2025-11-17T07:16:14.309Z",
    "metaData": {
        "teamId": "tea_b4rMsi2trB42WyuWP",
        "campaignId": "cam_eMZnxqs9Z9nqGxzwT",
        "leadId": "lea_o3uCcHsibhy9id8qD",
        "type": "emailsReplied",
        "createdBy": "usr_AzyCDxe92WNSrGkPz",
        "s3ready": false,
        "taskId": "tsk_AN9LqpP8AEWs2LH4D"
    },
    "campaignName": "NEW TO DELETE",
    "html": "<div dir=\"ltr\"><div>Hey Lucas, i’ve heard only good things about lemlist, let’s talk! Here’s my calendar: <a href=\"https://calendar.notion.so/meet/bvelitchkine/growth-eng\" style=\"color:inherit;text-decoration:inherit\" class=\"gmail-notion-link-token gmail-notion-focusable-token gmail-notion-enable-hover\" rel=\"noopener noreferrer\" tabindex=\"0\"><span style=\"text-decoration-line:underline;text-decoration-color:rgba(55,53,47,0.4);opacity:0.7\" class=\"gmail-link-annotation-unknown-block-id-1871970138\">https://calendar.notion.so/meet/bvelitchkine/growth-eng</span></a>. Cheers <span style=\"font-size:1em;font-family:&quot;Apple Color Emoji&quot;,&quot;Segoe UI Emoji&quot;,&quot;Segoe UI Symbol&quot;\">✌️</span></div><div><span style=\"font-size:1em;font-family:&quot;Apple Color Emoji&quot;,&quot;Segoe UI Emoji&quot;,&quot;Segoe UI Symbol&quot;\"><br></span></div><div><span style=\"font-size:1em;font-family:&quot;Apple Color Emoji&quot;,&quot;Segoe UI Emoji&quot;,&quot;Segoe UI Symbol&quot;\"><br></span></div><div><br></div></div><br><div class=\"gmail_quote gmail_quote_container\"><div dir=\"ltr\" class=\"gmail_attr\">On Mon, Nov 17, 2025 at 4:16 PM Lucille Rabaux &lt;<a href=\"mailto:[email protected]\">[email protected]</a>&gt; wrote:<br></div><blockquote class=\"gmail_quote\" style=\"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex\"><div style=\"min-width:360px\"></div><div dir=\"ltr\"><div dir=\"ltr\">\n    <div><div style=\"box-sizing:border-box\">hey, if you&#39;re a revops or gtm engineer, you should really checkout lemlist mate</div></div>\n    <div class=\"gmail_extra\">\n      <div class=\"gmail_signature\"><div dir=\"ltr\"><div><div dir=\"ltr\"></div></div></div></div>\n      \n    </div>\n    </div>\n<span summary=\"/api/reply/data-ll-tsk_AN9LqpP8AEWs2LH4D\"></span>\n<img alt=\"logo\" src=\"https://trail.joinlempire.com/api/track/open/usr_gmHgNGRcGPSTJrDbT/tsk_AN9LqpP8AEWs2LH4D\" height=\"1\" width=\"1\"></div><br>\n</blockquote></div>\n",
    "text": "Hey Lucas, i’ve heard only good things about lemlist, let’s talk! Here’s my\ncalendar: https://calendar.notion.so/meet/bvelitchkine/growth-eng. Cheers ✌️\n\n\nOn Mon, Nov 17, 2025 at 4:16 PM Lucille Rabaux <[email protected]>\nwrote:\n\n> hey, if you're a revops or gtm engineer, you should really checkout\n> lemlist mate\n> [image: logo]\n>\n>\n",
    "email": "[email protected]",
    "emailTemplateName": "Blank"
    }
]

Don’t forget to deactivate your workflow while developing, now that you have sample data!

Send the email content to OpenAI for sentiment analysis

This is where things get interesting: let’s create a tiny AI agent (based on an OpenAI) to classify leads’ replies!

Start by chaining the AI agent node with your lemlist trigger, selecting the “Define Below” option for your prompt, toggling the “Require Specific Output Format” option, and, finally, adding a “System Message” option to the node:
creating AI agent node in n8n

Fine-tune the AI agent basic configuration, to be similar to this:

Prompt:

A BDR at Lemlist received that response from a lead:

{{ $json.text }}

Is the lead interested or not?

System Message:

You're a SDR manager at Lemlist, a sales outreach SaaS that makes XDRs more productive.

From there, you have two things left to tell the agent:
1. what LLM to use (e.g. the least expensive ones from OpenAI because the task at hand is fairly easy)
  selecting OpenAI model
2. that we’re expecting a response in json format with a single “interested” key and a boolean value (true if the lead is interested, and false otherwise) by:
  1. using the “Structured Output Parser”
  2. selecting the “Define using JSON schema” option
  3. and actually defining the response schema
    defining output schema
  { "type": "object", "properties": { "interested": { "type": "boolean" } } }
Now:
1. add a manual trigger node
2. use the pinned data from the previous section as mock data in that node
3. connect it to your agent
4. execute the whole thing
5. make sure that you get the desired JSON output with a boolean that makes sense with the email reply (true if the email indicated interest, or false otherwise)
  testing AI agent
  Good? Pin the agent output and move on.

Mark the lead as interest or not in lemlist

“Wait, why even bother? We only want to send a notification in Slack right?”

Well, yes, but:

first, marking leads as (not) interested in lemlist is essential to analyse your campaign performances within lemlist
Someone (or something) needs to mark leads as interested or not to get these kinds of metrics and methodically improve your campaign
and, second, since we have already done the heavy lifting (classifying the replies as interested or not), we might as well mark them accordingly in lemlist — it’s an API call away: this endpoint to mark lead as interested or this one to mark them as not interested.

So, here’s what you’ll do:

make your workflow branch out depending on the agent’s response:
1. one branch for interested leads
2. another for non interested leads
  branching workflow based on AI response
In the first branch, you’ll add a new http node to make a custom api call to the first endpoint
Use the API reference playground to copy the curl of the request and paste it in the n8n node
Same thing in the second branch, with the endpoint to mark leads as not interested.
Finally, execute the workflow, check the results, pin the new output and move on.
executing workflow to mark lead in lemlist

Build a SDR-friendly notification and send it in a Slack channel

Here we are, last step of this tutorial! We’ll do two things:

manufacture a beautiful notification using Slack’s Block Kit Builder
send it in the dedicated channel in your slack workspace

Craft a SDR-friendly notification

Use the block builder to iterate on the notification and reach the desired result

Here's a SDR-friendly notification suggestion

And here's the JSON for that friendly suggestion

{
	"blocks": [
		{
			"type": "header",
			"text": {
				"type": "plain_text",
				"text": "💙 New interested lead in lemlist!",
				"emoji": true
			}
		},
		{
			"type": "divider"
		},
		{
			"type": "section",
			"fields": [
				{
					"type": "mrkdwn",
					"text": "*Campaign:*\n<https://app.lemlist.com/teams/team-id/campaigns-next/campaign-id/sequences/sequence-id/overview|EMEA RevOps Engage>"
				},
				{
					"type": "mrkdwn",
					"text": "*Sender:*\n[email protected] ;)"
				}
			]
		},
		{
			"type": "section",
			"fields": [
				{
					"type": "mrkdwn",
					"text": "*Lead Email:*\n<mailto:[email protected]|[email protected]>"
				},
				{
					"type": "mrkdwn",
					"text": "*LinkedIn URL:*\n<https://www.linkedin.com/in/bvelitchkine|https://www.linkedin.com/in/bvelitchkine>"
				}
			]
		},
		{
			"type": "section",
			"text": {
				"type": "mrkdwn",
				"text": "*Reply preview:*\n> Hey Lucas, i've hear only good things about lemlist, let's talk! Here's my calendar: https://calendar.notion.so/meet/bvelitchkine/growth-eng. Cheers ✌️"
			}
		},
		{
			"type": "actions",
			"elements": [
				{
					"type": "button",
					"text": {
						"type": "plain_text",
						"text": "Open in Inbox"
					},
					"url": "https://app.lemlist.com/teams/*your-team-id*/inbox/list/myConversations/contacts/*the-contact-id*",
					"style": "primary",
					"value": "open_inbox"
				}
			]
		}
	]
}

And here’s where you must go first, should you want to modify that notification ;)

Once you’re happy, add a “Edit Fields (Set)” node in your n8n workflow to extract all the variables required by above notification, namely:
- lemlist_team_id
- lemlist_campaign_id
- lemlist_campaign_name
- lemlist_lead_id
- lemlist_contact_id_of_the_lead
- lead_email
- lead_linkedin_url
- sender_email
- reply_preview
- lemlist_sequence_id
  Obviously do the same for all other variables (and change 'item' to 'first()' when needed).
Again, execute the node and pin the data.

Send that notification in Slack

Finally drop a “send message” Slack node in the n8n workflow, and configure it to send a message to yourself, as blocks:
configuring Slack node
Then, add the JSON blocks manufactured in the previous section in the dedicated area of the node, wrapped in a JSON.stringify() expression.
wrapping blocks in JSON.stringify

And then inject variables where needed (you will need to use javascript template literals):

Here’s the final n8n expression

Pay attention to JSON.stringify() and all the template litterals!

{{ JSON.stringify({
	"blocks": [
		{
			"type": "header",
			"text": {
				"type": "plain_text",
				"text": "💙 New interested lead in lemlist!",
				"emoji": true
			}
		},
		{
			"type": "divider"
		},
		{
			"type": "section",
			"fields": [
				{
					"type": "mrkdwn",
					"text": `*Campaign:*\n<https://app.lemlist.com/teams/${$json.lemlist_team_id}/campaigns-next/${$json.lemlist_campaign_id}/sequences/${$json.lemlist_sequence_id}/overview|${$json.lemlist_campaign_name}>`
				},
				{
					"type": "mrkdwn",
					"text": `*Sender:*\n${$json.sender_email}`
				}
			]
		},
		{
			"type": "section",
			"fields": [
				{
					"type": "mrkdwn",
					"text": `*Lead Email:*\n<mailto:${$json.lead_email}|${$json.lead_email}>`
				},
				{
					"type": "mrkdwn",
					"text": `*LinkedIn URL:*\n<${$json.lead_linkedin_url}|${$json.lead_linkedin_url}>`
				}
			]
		},
		{
			"type": "section",
			"text": {
				"type": "mrkdwn",
				"text": `*Reply preview:*\n> ${$json.reply_preview}`
			}
		},
		{
			"type": "actions",
			"elements": [
				{
					"type": "button",
					"text": {
						"type": "plain_text",
						"text": "Open in Inbox"
					},
					"url": `https://app.lemlist.com/teams/${$json.lemlist_team_id}/inbox/list/myConversations/contacts/${$json.lemlist_contact_id_of_the_lead}`,
					"style": "primary",
					"value": "open_inbox"
				}
			]
		}
	]
}) }}

Now, send the notification first to yourself, and once satisfied, change the node parameters so that future notifications are sent to the dedicated channel
Don’t forget to activate the workflow!

BONUS 👀

See how we’re injecting the sender’s email in the notification? Well, ideally, we’d like to tag the corresponding Slack user so that they’re specifically notified in Slack.So here’s your home assignment ;) try and tag that slack user, with a notification that looks slightly different:

That’s all folks!

Oh wait, no that’s not all 🙃 If you don’t want to start from scratch, you can get the full n8n workflow built in this guide here: Your n8n workflows Anyway, if you found that guide easy to follow, i suggest you move on to this one: Adding leads in a lemlist campaign in auto launch mode. It’s a nice complement to what you just built honestly.

User Guides

Send Slack notification upon lead positive reply

What you’ll learn in this guide

Imagine…

Warn SDRs in Slack when a lead seems interested

Overview: connect lemlist to Slack with OpenAI and n8n

Detect lead replies in lemlist instantaneously with n8n

Send the email content to OpenAI for sentiment analysis

Mark the lead as interest or not in lemlist

Build a SDR-friendly notification and send it in a Slack channel

Craft a SDR-friendly notification

Send that notification in Slack

That’s all folks!

User Guides

​What you’ll learn in this guide

​Imagine…

​Warn SDRs in Slack when a lead seems interested

​Overview: connect lemlist to Slack with OpenAI and n8n

​Detect lead replies in lemlist instantaneously with n8n

​Send the email content to OpenAI for sentiment analysis

​Mark the lead as interest or not in lemlist

​Build a SDR-friendly notification and send it in a Slack channel

​Craft a SDR-friendly notification

​Send that notification in Slack

​That’s all folks!

What you’ll learn in this guide

Imagine…

Warn SDRs in Slack when a lead seems interested

Overview: connect lemlist to Slack with OpenAI and n8n

Detect lead replies in lemlist instantaneously with n8n

Send the email content to OpenAI for sentiment analysis

Mark the lead as interest or not in lemlist

Build a SDR-friendly notification and send it in a Slack channel

Craft a SDR-friendly notification

Send that notification in Slack

That’s all folks!