One Unified Inbox for Outlook. Every reply answered in under 5 minutes.
Outlook and Microsoft 365 already run your mail on your own domain. Underfive connects straight to it when you sign in with Microsoft, with no third-party sequencer in between. Every reply to your outreach lands in one Unified Inbox, where AI inbox agents write a human-like response, send it from the same mailbox, follow up, and book the meeting on your calendar.
- 50 free replies
- No credit card
- Sign in with Microsoft, no webhook
Reply via Outlook 
Read & classified
Interested · drafted in 48s 
Outlook gets the reply. Your Unified Inbox wins the meeting.
Replies already arrive in your Outlook inbox. 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 across every mailbox and agents that answer in minutes.
Reply time, around the clock
Every reply to your outreach 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.
Webhooks. Sign in with Microsoft.
Connect each Outlook or Microsoft 365 mailbox with Microsoft sign-in. No sequencer, no webhook URL, no forwarding rules. Your Microsoft password is never stored by Underfive.
Connected in three steps
Sign in with Microsoft, add your warm-up phrases, and you are connected. No sequencer required.
Connect Outlook with Microsoft sign-in
In Underfive, choose Outlook under Integrations and sign in with the Microsoft account you send from. Microsoft grants Underfive read and send access to that mailbox, and your password stays with Microsoft.
- Microsoft sign-in, no third-party sequencer and no webhook
- Running hundreds of mailboxes? Book an onboarding call and we connect them in bulk
- Add your warm-up phrases so warm-up traffic never reaches the Unified Inbox
Integrations · Add tool Teach your inbox agents how you sell
Upload your offer, FAQs, pricing, and objection handling. Connect Outlook or Google Calendar. 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, the thread appears in your Unified Inbox. An inbox agent reads it, classifies it, writes a response in your voice, and sends it from the same Outlook mailbox. Interested prospects get a meeting on your calendar.
- Sent from the mailbox that received the reply, so the prospect sees one continuous thread
- Smart follow-ups when a thread goes quiet
- Every conversation in one Unified Inbox across mailboxes 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 sending from Microsoft 365? You are five minutes away.
Sign up, sign in with Microsoft, add your warm-up phrases, and the first reply that lands in your Outlook mailbox gets handled. Nothing changes in how you send.
What happens to each kind of reply
Your inbox agents classify every email 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.
Hundreds or thousands of mailboxes? We connect them for you.
Teams sending at volume rarely run a handful of mailboxes. They buy Microsoft mailboxes in bulk from providers like Zapmail, Inboxy, or MissionInbox. Do not sign in to each one by hand. Book an onboarding call and our team connects every mailbox to your Unified Inbox for you. Underfive is already integrated with Zapmail.
Book an onboarding callBulk onboarding, not one by one
Send us your mailbox list and we connect them at scale. No clicking through a Microsoft sign-in for every inbox.
Integrated with Zapmail
Using Zapmail for your Microsoft mailboxes? Underfive already works with Zapmail, so your mailboxes come across without manual setup.
Warm-up and ignore phrases
Add the subject lines or tags your warm-up tool uses, or connect your sequencer and Underfive pulls them in. Matching threads are removed from the Unified Inbox so agents only handle real replies.
A workspace per client
Running several brands or clients on separate Microsoft 365 domains? Give each its own Underfive workspace with its own agents, knowledge base, calendar, and Slack channel. Workspaces are unlimited on Agency.
Two tools. One job each.
Outlook owns sending and receiving on your domain. The Underfive Unified Inbox owns everything after the reply lands.
| Capability | Outlook | Underfive |
|---|---|---|
| Send and receive mail on your own domain | — | |
| Folders, rules, search, and storage | — | |
| Replies land in the mailbox that sent the email | ||
| One Unified Inbox across every mailbox 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 | — |
Outlook integration FAQ
Everything people ask before connecting.
How does the Outlook connection work? Is there a webhook?
No webhook. You sign in with Microsoft and Underfive gets read and send access to that mailbox. Underfive then watches the mailbox for replies and sends responses from it. Your Microsoft password is never stored by Underfive.
I have hundreds or thousands of Outlook mailboxes. Do I connect each one?
No. Most teams at that volume buy their Microsoft mailboxes from providers like Zapmail, Inboxy, or MissionInbox. Book an onboarding call and our team connects them in bulk. Underfive is already integrated with Zapmail.
Does Underfive reply from my Outlook mailbox?
Yes. Replies are sent from the same Outlook mailbox that received the reply, so the prospect sees one continuous thread from the same person.
Will this change how I send?
No. Keep sending from Outlook, Microsoft 365, or whatever sits in front of them exactly as you do today. Underfive only acts on replies.
What are warm-up phrases, and what about my personal mail?
Warm-up tools send automated emails through your mailbox. Add the subject lines or tags they use as warm-up phrases, or connect your sequencer and Underfive pulls them in. Threads that match are removed from the Unified Inbox, so agents only handle real replies.
Outlook already has an inbox. What does Underfive add?
Outlook shows one mailbox at a time. Underfive brings replies from every Outlook mailbox, every workspace, and every other tool into one Unified Inbox, and its inbox agents actually write and send the responses, follow up, and book meetings.
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.
Do you also support Gmail and Google Workspace?
Yes. Gmail and Google Workspace mailboxes connect with Google sign-in, and both land in the same Unified Inbox. See the Gmail integration page for details.
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.
Related reading
Stop leaving Outlook replies unanswered.
Sign in with Microsoft and connect in under five minutes, or book an onboarding call and we connect every mailbox for you. Your first 50 replies are free.
Not on Microsoft 365 yet? Learn about Microsoft 365.