The Unified Inbox That Turns
Replies Into Meetings.
Underfive brings every reply from your cold email and LinkedIn tools into one Unified Inbox. AI inbox agents read each one, send human-like responses in under 5 minutes, follow up, negotiate times, and send calendar invites on your behalf.
Sound familiar?
Underfive fixes all five.
- Lead replies sit unanswered for hours
- Back-and-forth scheduling wastes everyone's time
- You miss the 5-minute response window
- No one follows up after the first reply
- Interested leads never get a meeting booked
more likely to qualify a leadwhen you reply within an hour
Underfive answers every reply in under 5 minutes, 24/7.
Source: Harvard Business Review, “The Short Life of Online Sales Leads,” 2011. Qualified means reaching a decision maker, not a closed sale.
Works With Tools You Already Use
Seamlessly plug into your existing outbound stack. No complicated setup, no migration hassles.
Don't see your tool? Let us know and we'll add it.
How Underfive Works
Connect your outbound tools, teach your inbox agents, and every reply in your Unified Inbox gets a human answer in under five minutes.
Connect your outbound tools
Paste an API key from PlusVibe, Email Bison, Smartlead, Instantly, Lemlist or HeyReach, or connect Gmail and Outlook. Underfive registers the reply webhook for you, and every reply starts landing in one Unified Inbox.
- One API key per tool, no webhook URLs to copy
- Email and LinkedIn replies in the same inbox
- Each client and campaign in its own workspace
PlusVibe
Email Bison
Smartlead
Instantly
Lemlist
HeyReach
GetSales.io
GmailSet up your inbox agents
Point the agent at your website and docs, connect your calendar, and decide which replies send on their own and which wait for your approval.
- Knowledge learned from your site, pricing and FAQs
- Auto-send or Require Approval, per reply category
- Google Calendar or Outlook connected for booking
Connect calendarEvery reply answered in under 5 minutes
When a lead replies, the inbox agent reads the whole thread, writes a human-like answer, sends it from the original mailbox or LinkedIn profile, and books the meeting. Quiet threads get a smart follow-up.
- Human-like replies in under 5 minutes, 24/7
- Meetings booked straight onto your calendar
- Smart follow-ups when a thread goes quiet
PlusVibeEmail BisonSmartleadInstantlyLemlistHeyReachGetSales.ioGmailSetup takes under 5 minutes. No credit card required.
Transform Your Lead Management
Our platform delivers real business results through human-like automated conversations
Take inbox triage off your plate
Automate email responses and follow-ups that would otherwise take hours of manual work.
Reply inside the five-minute window
Engage leads within 5 minutes of their inquiry, when they're most interested.
Book meetings without the back-and-forth
Automatic scheduling links and intelligent follow-ups, handled for you.
Never let a warm reply go cold
Every reply gets a personalized, instant response instead of sitting in a queue.
Trusted by Growing Businesses
See what our customers are saying about Underfive
"We are now using Underfive full-time for our inbox management, and we wanted to thank you for being so quick and attentive to our feature requests and bug reports. You guys are really on the ball and have gotten the product to a point that it's fulfilling our original vision. A big THANK YOU for being fast, attentive, listening to our feedback, and implementing our requests. We are really happy with Underfive!"
Agency Owner
Manages 20 Client Workspaces on Underfive
"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!"
Erik Paulson
Founder, Vendisys
"This tool has exceeded my expectations! I use SmartLead and the quality of replies that Underfive generates, combined with the reply agent configuration, is exactly what I was looking for."
Suprava Sabat
Founder, AcquisitionX
Frequently Asked Questions
Got questions? We've got answers
Reply playbooks, every week
How outbound teams answer, follow up and book from the replies they already get.
LatestHeyReach Reply Management: Running a LinkedIn and Email Reply Desk at Agency Scale
HeyReach reply management at agency scale: what the unibox does well, the privacy setting that hides replies, and how to work LinkedIn and email in one inbox.
Unified Inbox for Cold Email: What It Is, Why One Inbox Per Tool Breaks, and How to Evaluate One
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Email Bison Reply Management: The Agency Playbook for Answering Every Reply in Under Five Minutes
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Cold Outreach During the Holidays: How to Handle December Replies and Load Q1 Pipeline
8 min readEvery reply answered in under 5 minutes. Starting today.
Connect your outbound tools to one Unified Inbox and let inbox agents answer, follow up, and book the meeting while your team takes the calls.
- No credit card required
- Free 14-day trial
- Unlimited agents and seats
- 1 Paste your API key 0:00
Connect your sending tool. The webhook sets itself up.
- 2 Teach your inbox agent 2:00
Paste your website, add your calendar, pick what auto-sends.
- First reply answered 4:30
The next lead who replies gets an answer in minutes.
