Official PlusVibe partner. PlusVibe users get 200 free agent credits on our Professional plan, 4x our standard trial. Underfive users get 15% off PlusVibe for 3 months with code UNDERFIVE15 at plusvibe.ai.
One Unified Inbox for PlusVibe. Every reply answered in under 5 minutes.
PlusVibe gets your cold email into the primary inbox. Underfive takes it from there. 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.
- 50 free replies
- No credit card
- Webhook created for you
Reply via PlusVibe
Read & classified
Interested · drafted in 48s 
PlusVibe lands the email. Your Unified Inbox wins the meeting.
Dedicated IPs and a private warm-up pool get you into the primary 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 and agents that answer in minutes.
Reply time, around the clock
Every reply to a PlusVibe 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). PlusVibe gets you into the primary inbox. Underfive makes the five-minute window.
API key. That is the whole setup.
Paste your PlusVibe API key and Underfive registers the reply webhook for you. No URLs to copy between tabs, no changes to your campaigns.
Connected in three steps
One API key. No webhook URLs to copy. No changes to your campaigns.
Paste your PlusVibe API key
Copy the API key from your PlusVibe workspace settings and paste it into Underfive under Integrations. Underfive creates the reply webhook in PlusVibe for you and starts listening for replies straight away.
- One API key per PlusVibe workspace
- Webhook created and verified automatically
- Nothing to configure inside PlusVibe
Integrations · Add tool PlusVibe 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, PlusVibe 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 PlusVibe from the same inbox. Interested prospects get a meeting on your calendar.
- Sent from the inbox that received the reply, so deliverability stays with PlusVibe
- 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 PlusVibe? You are three minutes away.
Sign up, paste your API key, and the first reply that lands in your PlusVibe workspace gets handled. Nothing changes in your sequences, inboxes, warm-up, or IPs.
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.
Private infra per client. One inbox for all of them.
PlusVibe was built for agencies that cannot share infrastructure between clients. Underfive mirrors that structure on the reply side, so each client gets its own agents, knowledge base, calendar, and Slack channel, and every client's replies show up in one view.
Isolated infra per client, one inbox across them
PlusVibe gives each client its own sending servers and connector IPs. Underfive gives each client its own workspace, inbox agents, and knowledge base, and rolls every reply up into one Unified Inbox.
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 PlusVibe workspace per client.
Trigger keywords for shared workspaces
Running several offers through one PlusVibe 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 on the reply side either.
Two tools. One job each.
PlusVibe owns sending, warm-up, and deliverability. The Underfive Unified Inbox owns everything after the reply lands.
| Capability | PlusVibe | Underfive |
|---|---|---|
| Dedicated IPs, private warm-up pool, deliverability monitoring | ||
| Sequences, A/B tests, AI icebreakers, lead enrichment | ||
| Replies collected with sentiment and intent | ||
| 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 |
“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.”
PlusVibe integration FAQ
Everything people ask before connecting.
Do I have to set up a webhook in PlusVibe manually?
No. When you paste your PlusVibe API key into Underfive, Underfive registers the reply webhook in your PlusVibe workspace for you. There are no URLs to copy and nothing to configure inside PlusVibe.
Where do I find my PlusVibe API key?
In your PlusVibe workspace settings, under the API section. Each PlusVibe workspace has its own key, so connect each workspace to Underfive separately if you run multiple clients.
Does Underfive reply from my PlusVibe inboxes?
Yes. Replies are sent through PlusVibe from the sender inbox that received the reply, so the prospect sees one continuous thread from the same person. Your dedicated IPs, warm-up, and deliverability settings stay in PlusVibe.
Will this change my PlusVibe campaigns?
No. Campaigns, sequences, schedules, warm-up, and inboxes keep running exactly as they do today. Underfive only acts on replies.
PlusVibe already shows replies with sentiment. What does Underfive add?
PlusVibe collects and labels the replies inside that workspace. Underfive brings replies from every PlusVibe workspace and every other tool into one Unified Inbox, and its inbox agents actually write and send the response, follow up, and book the meeting.
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 PlusVibe. How does that work?
Create one Underfive workspace per PlusVibe 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.
What does it cost?
Start with 50 free replies and no credit card. After that, plans are priced by agent credits. PlusVibe has its own 14-day free trial, also without a credit card.
Stop leaving PlusVibe replies unanswered.
Connect in under five minutes. Your first 50 replies are free, and nothing changes in your campaigns.
Not on PlusVibe yet? Start a free 14-day PlusVibe trial, no credit card needed.