Compare · Smartlead's AI agent
Underfive vs Smartlead's AI agent. One Unified Inbox for every platform.
Smartlead's AI agent replies to leads inside Smartlead. If Smartlead is your only sending tool, that may be all you need. Underfive is a Unified Inbox that sits above your tools. Replies from Smartlead, Instantly, Email Bison, and HeyReach land in one place, and AI inbox agents answer email and LinkedIn DMs in under 5 minutes. Add or switch platforms and your agents, knowledge base, and rules stay the same.
- 50 free replies
- No credit card
- Works with Smartlead
Same reply, to a campaign you run outside Smartlead. What happens next.
Smartlead's AI agent 
Lena Schulz 
via Instantly Happy to take a look. Can you send over some times for next week?
- Reply lands
This campaign runs in Instantly. Smartlead's AI agent works inside Smartlead, so it does not see this thread.
- Then it waits
The reply sits in Instantly's inbox until a person answers it.
- For Smartlead campaigns
A reply to a Smartlead campaign can be answered by Smartlead's agent, inside Smartlead.
Underfive Unified Inbox Lena Schulz via Instantly Happy to take a look. Can you send over some times for next week?
- Reply lands
It arrives in the Unified Inbox, next to replies from Smartlead, Email Bison, and HeyReach.
- Under 5 minutes
An inbox agent offers real times from your calendar. Sent through Instantly, from the same mailbox.
- Booked
Lena picks a time. The invite goes out and your team is notified in Slack.
Feature by feature, without the spin
Both reply to cold email leads and book meetings. The difference is where they work.
| Feature | Smartlead's AI agent | Unified Inbox |
|---|---|---|
| Replies to cold email leads | Yes | Yes |
| Human-like responses | Yes | Yes |
| Calendar booking | Yes | Yes |
| Smart follow-ups | Yes | Yes |
| Works with Smartlead | Yes | Yes |
| Works with Instantly | No | Yes |
| Works with Email Bison | No | Yes |
| Works with HeyReach | No | Yes |
| Replies to LinkedIn DMs | No | Yes |
| One Unified Inbox across platforms and clients | No | Yes |
| Replies in under 5 minutes, 24/7 | No | Yes |
| Unlimited inbox agents | No | Yes |
| One Workspace Agent per workspace | No | Yes |
| Review and approve replies from Slack | No | Yes |
| Sentiment analysis on every reply | No | Yes |
| Keep your agents when you switch sending tools | No | Yes |
The Smartlead column reflects our understanding of Smartlead's AI agent. Products change, so check Smartlead for its current feature list.
Where one inbox for every platform matters
An agent tied to one sender works until your outbound grows past that sender.
You run more than one sending tool
Many agencies use Smartlead for some clients and Instantly for others. With Underfive, every reply from every platform lands in one Unified Inbox, and inbox agents answer each client's leads.
You run cold email and LinkedIn
Sending LinkedIn DMs through HeyReach alongside cold email? The same Unified Inbox handles both, and replies go out from the same mailbox or LinkedIn profile.
You might switch platforms
Moving from Smartlead to Instantly, or the other way? Your inbox agents, knowledge base, and rules stay in Underfive. Connect the new tool and keep going.
You want room to add tools
New outreach tools launch all the time. Underfive keeps adding integrations, so the reply layer does not depend on any single sender.
Email Bison
LinkedIn via HeyReachWhen Smartlead's AI agent is the right call
A built-in agent is a sensible choice for a simple setup. Here is when to stay with it.
Smartlead is your only sending tool
If every campaign runs in Smartlead and you plan to stay, an agent built into Smartlead covers every reply you get.
You only run cold email
No LinkedIn outreach means no DMs to answer. A cold email agent inside your sequencer is a reasonable fit.
You want one product
Sending and replying in the same tool means one login, one vendor, and one place to configure. That simplicity has real value.
You run one workspace
A single team with a single offer has less need for one inbox across platforms and clients.
Keep Smartlead. Add the Unified Inbox.
Underfive is not a Smartlead replacement. Smartlead sends. The Unified Inbox handles what comes back.
Smartlead keeps sending
Campaigns, warm-up, and deliverability stay exactly where they are. Underfive does not replace Smartlead.
Connect in two pastes
Your Smartlead API key goes into Underfive. Your Underfive webhook URL goes into Smartlead. Nothing in your campaigns changes.
Agents answer from one inbox
Replies land in the Unified Inbox. Inbox agents respond through Smartlead from the same mailbox, in under 5 minutes.
Underfive vs Smartlead's AI agent FAQ
What is the difference between Underfive and Smartlead's AI agent?
Smartlead's AI agent replies to leads inside Smartlead. Underfive is a Unified Inbox that works across Smartlead, Instantly, Email Bison, and HeyReach. Its AI inbox agents answer cold email and LinkedIn DM replies in under 5 minutes, from one place.
Does Underfive work with Smartlead?
Yes. Smartlead keeps sending your campaigns. You paste your Smartlead API key into Underfive and your Underfive webhook URL into Smartlead. Nothing in your campaigns changes, and replies go back out through Smartlead from the same mailbox.
Do I have to leave Smartlead to use Underfive?
No. Underfive does not send campaigns. It handles the replies. Your sequencer keeps doing sending, warm-up, and deliverability.
When is Smartlead's AI agent enough?
If Smartlead is your only sending tool, you only run cold email, and you want sending and replying in one product, its built-in agent may be all you need.
What happens if I switch from Smartlead to another tool?
Your inbox agents, knowledge base, and rules stay in Underfive. Connect the new sending tool and the same agents keep answering replies.
Does Underfive handle LinkedIn replies too?
Yes. The Unified Inbox takes LinkedIn DM replies from HeyReach, Aimfox, Expandi, GetSales, and Lemlist, and answers them from the same LinkedIn profile.
How many inbox agents can I run?
Unlimited. Every plan includes unlimited inbox agents and team members. You pay per reply handled, not per agent or seat. Start with 50 free replies and no credit card.
One inbox for every platform you send from.
Connect Smartlead and anything else you run. Inbox agents answer every reply in under 5 minutes. Your first 50 replies are free.