An AI appointment setter for cold email, replying from the same mailbox.
An AI appointment setter for cold email reads every reply to your campaigns and turns interested ones into meetings. Underfive connects to Smartlead, Instantly, Email Bison, PlusVibe, Lemlist, Gmail and Outlook, answers in under 5 minutes from the mailbox the prospect replied to, proposes real times and books the call.
50 free credits · no credit card · updated October 2026
Cold email replies are messy: auto-replies, referrals, "who are you?", "send pricing". Sorting them across dozens of mailboxes is where interested leads get lost. Underfive sorts every reply and answers the ones that matter.
How does it work?
- 1
Connect your sending tool
An API key or OAuth connection. Replies from every mailbox start landing in one inbox.
- 2
Every reply is categorised
Interested, meeting request, question, out of office, not now, unsubscribe and more.
- 3
Interested ones get booked
An answer in your voice from the same mailbox, real times, and an invite.
How does it compare?
| Underfive | Sequencer master inbox | Forward to a rep | |
|---|---|---|---|
| Answers the reply | Yes, in under 5 minutes | No, you do | When the rep sees it |
| Same mailbox and thread | Yes | Yes | Often not |
| Works across tools | All in one inbox | One tool only | Email forwarding |
| Books the meeting | Yes | No | Manually |
| Follows up | Automatically | Sequence only | Rarely |
What you get with Underfive
Every major sequencer
Smartlead, Instantly, Email Bison, PlusVibe, Lemlist, Gmail and Outlook.
Deliverability-friendly
Replies go out in the existing thread from the original mailbox, never from a new domain.
No cap on mailboxes
Connect every sending inbox, including Azure and Outlook tenants.
Out-of-office aware
OOO replies are read and the follow-up waits until they are back.
Learn more Smartlead →Instantly →Email Bison →
Frequently asked questions
Which cold email tools does it work with?
Smartlead, Instantly, Email Bison, PlusVibe, Lemlist, Gmail and Outlook, with more added regularly.
Does it reply from my sending mailbox?
Yes. Each answer goes out from the mailbox the prospect replied to, in the same thread.
What happens with out-of-office replies?
They are categorised as out of office, and follow-ups wait until the prospect is back.
How many mailboxes can I connect?
There is no cap on mailboxes connected through your sending tools.
Can it handle pricing questions?
Yes, from your knowledge base. You can also require approval on pricing replies before they are sent.