One Unified Inbox for Email Bison. Every reply answered in under 5 minutes.
Underfive plugs into Email Bison with one API key. Every reply from every campaign and client lands in one Unified Inbox, where AI inbox agents write a human-like response, send it from the same sender, follow up, and book the meeting on your calendar. Your campaigns keep running exactly as they do today.
- 50 free replies
- No credit card
- Webhook created for you
Reply via Email Bison
Read & classified
Interested · drafted in 48s 
Email Bison gets the reply. Your Unified Inbox wins the meeting.
Your sending stack is already excellent. The expensive gap is the hours between a prospect replying and someone on your team finding it, reading it, and writing back. Underfive closes that gap with one inbox and agents that answer in minutes.
Reply time, around the clock
Every reply to an Email Bison campaign gets a human-like response in under five minutes. Nights, weekends, and holidays included.
More likely to qualify the lead
Harvard Business Review found that firms contacting a lead within an hour were nearly seven times more likely to qualify it, meaning they reached a real decision maker, than firms that waited an hour longer (Oldroyd, McElheran and Elkington, HBR, March 2011). That window is the whole product.
Manual webhook steps
Paste your Email Bison API key and Underfive registers the webhook in your workspace for you. Nothing to copy between tabs.
Connected in three steps
One API key. No webhook URLs to copy. No changes to your campaigns.
Paste your Email Bison API key
In Email Bison, open Settings and then Developer API to copy a key. Paste it into Underfive under Integrations. Underfive calls the Email Bison API to create a webhook named "Underfive" in your workspace, subscribed to the Contact Replied event.
- One API key per Email Bison workspace
- Webhook created and verified automatically
- Email Bison retries delivery up to 5 times over 24 hours if a call fails
Teach your inbox agents how you sell
Upload your offer, FAQs, pricing, and objection handling. Connect Google Calendar or Outlook. Then decide which reply categories send automatically and which wait for a human.
- Knowledge base and reply logic per workspace
- Auto-send or Require Approval, per category
- Calendar connected for direct booking
Replies are answered, followed up, and booked
When a prospect replies, Email Bison sends the thread to your Unified Inbox. An inbox agent reads it, classifies it, writes a response in your voice, and sends it back through Email Bison from the same inbox. Interested prospects get a meeting on your calendar.
- Sent from the inbox that received the reply
- Smart follow-ups when a thread goes quiet
- Every conversation in one Unified Inbox across campaigns and clients
Unified Inbox- Meeting bookedJordan MeyerThursday at 10:30 works. Talk then.Meeting booked
-
Replied · autoEmily TranCan you send over a case study first?Replied · auto -
Follow-up · Apr 2Omar HaddadWe're mid-contract until Q2, circle back then?Follow-up · Apr 2 -
Needs approvalLena SchulzWho else at your company should I loop in?Needs approval
Already on Email Bison? You are three minutes away.
Sign up, paste your API key, and the first reply that lands in your Email Bison workspace gets handled. Nothing changes in your sequences, inboxes, or warm-up.
What happens to each kind of reply
Your inbox agents classify every reply before they act. You decide which categories auto-send and which wait for a human.
Interested
Answers, proposes times, and books the meeting on your calendar.
Pricing question
Replies with the pricing guidance from your knowledge base and moves toward a call.
Product question
Answers from your FAQs and offer details, in your tone of voice.
Objection
Handles the objection using your playbook and keeps the thread alive.
Not right now
Acknowledges, then schedules a follow-up for the timeframe they gave.
Referral
Thanks them and continues the conversation with the person they named.
Not interested
Closes politely and stops the thread. No more follow-ups.
Uncategorized
Goes to the approval queue so a human decides. Nothing is sent blind.
Categories and their behaviour are yours to edit per workspace. Nothing is sent without a category you approved.
Same workspace model. Zero extra seats.
Email Bison was built for teams running many clients from one account. Underfive mirrors that structure: each client gets its own inbox agents, knowledge base, calendar, and Slack channel, and every client's replies roll up into one Unified Inbox without a per-seat bill.
One workspace per client, on both sides
Email Bison separates clients into workspaces. Underfive does the same. Connect each Email Bison workspace to its own Underfive workspace with its own API key, agent, and knowledge base.
Workspace Agent
Turn it on for a workspace and the agent handles every positive reply in that workspace without trigger keywords. Built for agencies running one Email Bison workspace per client.
Trigger keywords for shared workspaces
Running several offers through one Email Bison workspace? Route replies to the right agent by keyword, such as a brand name or domain in the thread.
A workspace per client
Team members are unlimited on every plan and workspaces are unlimited on Agency, so adding a client never adds a per-seat fee. The Unified Inbox shows every client in one view.
Two tools. One job each.
Email Bison owns sending and deliverability. The Underfive Unified Inbox owns everything after the reply lands.
| Capability | Email Bison | Underfive |
|---|---|---|
| Sending infrastructure, warm-up, deliverability | — | |
| Sequences, A/B tests, lead storage | — | |
| Reply threads stored in one place | ||
| One Unified Inbox across every workspace and client | — | |
| Writes a human-like reply to each response | — | |
| Replies within 5 minutes, 24/7 | — | |
| Negotiates times and books the meeting | — | |
| Follows up when a thread goes quiet | — | |
| Approval queue with Slack notifications | — |
“Underfive has been a game-changer for us! Thank you to the team for integrating it with Email Bison as per our request. The reply agent truly lives up to its name - under five minutes every time!”
Watch the full setup
From a blank Underfive account to the first Email Bison reply handled, in one short recording.
Prefer reading? Open the Underfive docs.
Email Bison integration FAQ
Everything people ask before connecting.
Do I have to set up a webhook in Email Bison manually?
No. When you paste your Email Bison API key into Underfive, Underfive uses the Email Bison API to create a webhook named "Underfive" in your workspace and subscribes it to the Contact Replied event. You can see it in Email Bison under Settings and then Webhooks.
Where do I find my Email Bison API key?
In Email Bison, open Settings and then Developer API to create or copy a key. Each Email Bison workspace has its own key, so connect each workspace to Underfive separately if you run multiple clients.
Does Underfive reply from my Email Bison inboxes?
Yes. Replies are sent through Email Bison from the sender inbox that received the reply, so the prospect sees one continuous thread from the same person. Your sending infrastructure, warm-up, and deliverability settings stay in Email Bison.
Will this change my Email Bison campaigns?
No. Campaigns, sequences, schedules, and inboxes keep running exactly as they do today. Underfive only acts on replies.
Can I review replies before they go out?
Yes. Each reply category can be set to auto-send or require approval. Replies that need approval wait in your Underfive queue, and you can approve them from the app, from Slack, or through the Underfive MCP connector.
I run several clients on Email Bison. How does that work?
Create one Underfive workspace per Email Bison workspace and connect each with its own API key. Turn on the Workspace Agent so it handles every positive reply in that workspace. Team members are unlimited on every plan, workspaces are unlimited on Agency, and the Unified Inbox shows every client in one place.
How fast does Underfive reply?
Under five minutes, 24 hours a day, including weekends. The agent reads the thread, classifies it, drafts a response, and sends it through Email Bison.
What does it cost?
Start with 50 free replies and no credit card. After that, plans are priced by agent credits. See the pricing page for current plans.
Stop leaving Email Bison replies unanswered.
Connect in under five minutes. Your first 50 replies are free, and nothing changes in your campaigns.
Not on Email Bison yet? Learn about Email Bison.