Run outbound without living in your inbox.
Underfive is a Unified Inbox for founder-led outbound. Every reply from every campaign lands in one place. Inbox agents answer in under 5 minutes, even at 2 AM, follow up, and put the meeting on your calendar. You review only what matters.
- 50 free replies
- No credit card
- Setup in under 5 minutes
Unified Inbox · While you were asleep- 2:04 AM
Emily Tran 
via Smartlead Interesting. Is this a fit for a team of twelve?
- 2:07 AMInbox agent replied Product question Auto-sendIt is, Emily. Teams that size are who we built it for. Worth 15 minutes to walk through it? Thursday 10:30 or Friday 2:00 your time?
- 2:31 AM
Thursday 10:30 works.
- 2:32 AM
Invite sent from your calendarThu 10:30 · thread tagged Meeting Scheduled
Four jobs you hand off on day one
Founder-led outbound works until the replies start coming in. Then the inbox becomes a second job. These are the parts you give away.
Stop replying at midnight
Inbox agents answer every reply in under 5 minutes, 24 hours a day, weekends included. The reply goes out from the same mailbox the prospect wrote to, in their language.
Inbox agentsStop chasing quiet threads
When a prospect goes silent after a reply, the agent follows up in the context of the thread. A "circle back in Q2" gets a follow-up in Q2. It stops the moment they answer or say no.
Smart follow-upsStop playing calendar ping-pong
An interested prospect gets two real times from your calendar, in their time zone. The agent negotiates, sends the invite from Google Calendar or Outlook, and tags the thread Meeting Scheduled.
Meeting bookingStop reading every reply
Choose which reply categories send on their own and which wait for you. Anything the agent cannot classify waits too. Clear the queue from the app or from Slack on your phone.
ApprovalsReview only what matters.
Every reply category sits in one of two buckets. Routine replies go out on their own. The ones you care about wait for you, with the draft already written.
A reply the agent cannot classify is never guessed at. It waits in the queue and you decide.
Approve in the app 
Or in Slack, on your phone How it works for founders
Four steps, under five minutes. No sales ops hire, no implementation call.
Connect your sending tool
Smartlead, Instantly, Email Bison, PlusVibe, HeyReach, or Gmail. Replies start landing in your Unified Inbox.
Paste your website
Underfive drafts your company description from it. Add your offer, pricing guidance, FAQs, and a case study or two. Edit anything.
Connect your calendar
Google Calendar or Outlook, natively. Set your meeting length and availability. Already on Calendly or Cal.com? Add the link as an alternative.
Pick what needs you, then launch
Drag reply categories between Auto-send and Require Approval. Start with everything on approval if you want to watch first.
and more Three ways to handle the replies
Sending is the easy part. Somebody still has to answer.
Answer every reply yourself
Does: Nobody knows the product better, and the first few replies are worth reading.
Gap: Replies wait while you build, sell, and fundraise. Nights and weekends go unanswered. Follow-ups depend on your memory.
Hire an SDR
Does: Puts a person on the inbox full time.
Gap: A salary, a hiring process, and weeks of ramp before the first good reply. Still offline at 2 AM.
A Unified Inbox with inbox agents
Does: Every reply from every campaign in one view, answered in under 5 minutes by agents trained on your offer.
- Replies in under 5 minutes, 24/7
- Follows up until they answer or say no
- Books meetings on your calendar
- You approve what you choose to
- Live in under 5 minutes
"After running a lead generation agency and managing 1M+ outbound emails and DMs every month, I built Underfive using the same inbox workflows, reply logic, and booking systems my team relies on every day."
Unified Inbox for founders FAQ
What is a Unified Inbox for founders?
It is one view of every reply from every outbound campaign you run. Underfive is a Unified Inbox with AI inbox agents inside it. The agents answer each reply in under 5 minutes, follow up, and book meetings on your calendar, so you can run outbound at volume and only review what matters.
Do I need to hire an SDR to run outbound?
Not to handle replies. Inbox agents take first responses, questions, objections, follow-ups, and scheduling. You keep the calls and any reply category you want to approve yourself.
How long does setup take?
Under 5 minutes. Connect your sending tool, paste your website so Underfive can draft your company description, connect Google Calendar or Outlook, choose which reply categories need your approval, and launch.
What happens when a lead replies at 2 AM?
An inbox agent reads the thread, classifies the reply, and answers in under 5 minutes from the same sender. If the prospect is interested, it proposes two times from your real availability, in their time zone, and sends the invite once they agree.
Will the replies sound like me?
The agent writes from your knowledge base and reply logic, in the tone you set, and references the actual thread and your actual offer. It does not send templates. You can review drafts before launch and keep any category on approval.
Can I check every reply before it goes out?
Yes. Put every reply category on Require Approval and each draft waits for you. Approve, edit, or reject from the app, from Slack, or through the MCP connector. Move categories to Auto-send as you gain confidence.
Does it replace Smartlead, Instantly, or Email Bison?
No. Your sending tool keeps doing sending, warm-up, and deliverability. The Unified Inbox takes over the moment a reply lands and answers through the same tool and sender.
What does it cost?
Start with 50 free replies and no credit card. After that, plans are priced by agent credits and include unlimited team members and inbox agents, with workspaces from 1 on Professional to unlimited on Agency. Understanding a reply costs half a credit, drafting a reply costs one, and calendar invites cost nothing.
Wake up to meetings, not an inbox.
Set up in under five minutes. Your first 50 replies are free, with no credit card.