SC
Sarah Chen [email protected]
Thanks for sending over the docs. I've reviewed them and have a few questions. Can we sync up tomorrow morning?
Open source
Self-host the platform · Apache 2.0 Apache 2.0
The largest open-source cold email platform.
Warmbly warms your mailboxes, sends your campaigns, and triages every reply. Run it on our cloud or self-host the whole thing on yours.
Free forever when you self-host. When Warmbly Cloud launches, a hosted workspace starts free with 10 mailboxes and warmup, and linked instances get their warmup run for them.
Warmbly
A Acme
Accounts
Growth
28ms
Accounts 128 mailboxes
Total
128
connected
Healthy
122
sending now
Warming
6
ramping up
Needs attention
0
paused / fail
Mailboxes 128
Search by email…
| Account | Sent | Warmup | Status | ||
|---|---|---|---|---|---|
| 37 | 22 | healthy | |||
| 24 | 18 | healthy | |||
| 46 | 34 | healthy | |||
| 18 | 12 | warming |
github.com/warmbly/warmbly · Apache 2.0 · Run it on our cloud or your own infra · Go · Rust · Elixir · React
Campaigns
Sequences that branch on real behavior.
Build a multi-step flow on the canvas, then drag a connector from any step to fork on opens, clicks, and replies. It's the exact builder you'll use in the app.
Drag to branch
Pull a link from a step to add an “if opened / clicked / replied” path. No match just stops.
A/B at every step
Weighted subject + body variants; the stronger one keeps sending.
Threaded follow-ups
Follow-ups reply on the previous subject, so they land in the same conversation.
app.warmbly.com/campaigns/q1-sales/sequences
Q1 Sales Outreach
draftcmp_8fK2pQ7rXa19
Overview
Leads
Steps
Schedule
Settings
Stop on reply
wait 2d else
First email Start
Email
Quick question, {{.FirstName}}
if opened within 3d
Follow-up
Email
Following up on my message
Alternative
Email
Trying a different angle
Add engagement tag
Add tag
engaged
Ends here
Stop
Scheduling
Send only inside their working hours.
A calendar-style editor with full per-day control. Draw a sending window on any weekday, drag to move it, grab an edge to resize. Everything snaps to 30 minutes.
Per-day windows
Independent windows for each day: mornings only, or split shifts. Several per day is fine.
Timezone-aware
Sends follow the chosen timezone; worker IPs spread the volume naturally.
One-click presets
Mon–Fri 9–5 in a tap, then fine-tune by dragging the blocks.
app.warmbly.com/campaigns/q1-sales/schedule
Weekly sending windows
7 windows across 5 days
Presets Drag to add · drag a block to move · edges to resize · ⧉ copies a day to all
Mon
Tue
Wed
Thu
Fri
Sat
Sun
12a 3a 6a 9a 12p 3p 6p 9p 12a
9am
12pm
12pm
1pm
5pm
5pm
9am
5pm
5pm
8:30am
12pm
12pm
2pm
6pm
6pm
9am
5pm
5pm
9am
3pm
3pm
drag, or tap +
drag, or tap +
Each day is independent. Set different windows per day, or several windows in one day. Sends are scheduled in America/New York; worker IPs spread distribution naturally.
Campaign dates Jun 9 – Jul 7, 2026 28 days
Start date
End date
Optional bounds for when the campaign may send. Leave both blank to run open-ended.
Unified inbox
Every reply, triaged the moment it lands.
Replies from every connected mailbox stream into one searchable queue. The classifier tags each one on arrival so you act on the labels that matter.
One queue, every mailbox
Scope by inbox, tag, or status: unread, awaiting reply, snoozed, scheduled.
Classified on arrival
Positive, out-of-office, unsubscribe and bounce are labeled before you open them.
Reply in place
Snooze, schedule, and send from the same pane, keyboard-first.
app.warmbly.com/unibox
7 unread
3 awaiting
24 today
89 week
2 snoozed
3 mailboxes
live
Search inbox… (/)
Today 4
SC
Sarah Chen 5m
Follow up on Q1 proposal
Thanks for sending over the docs. I've reviewed them and have a few…
JS
Jordan Smith 42m
Re: Dashboard integration
The API endpoint looks good. When can we expect the staging build?
AM
Alex Morgan 3h
New partnership opportunity
Hi there, I'm reaching out about a potential partnership between…
[email protected] Leads
CR
3 messages 2
YO
14:15 Absolutely! How does 10am EST work for you?
SC
Sarah Chen [email protected]
Perfect. See you then!
Forward
Hover any message to reply to it directly.
Analytics
Proof of what actually landed.
Deliverability across the whole workspace: sent, opens, clicks, replies and bounces, with per-campaign breakdowns and account health on one screen.
Placement, not vanity
Track the metrics that move reputation, over 7, 30 or 90 days.
Best performers, surfaced
Top campaigns and account health rank themselves as sends roll in.
Shareable report card
Export a branded image of any range in a single tap.
app.warmbly.com/analytics
Analytics Deliverability across the workspace
Total sent
2,847
in range
Open rate
31.3%
after delivery
Reply rate
2.0%
incl. positive
Bounce rate
0.5%
hard + soft
Email performance
Dec 2 Dec 8
Top campaigns
All campaigns
Q4 Outreach - Tech Leaders 850 sent 38.5% open 2.8% reply
Win-back: Former Customers 620 sent 26.3% open 1.6% reply
Product Launch Beta Access 480 sent 42.1% open 3.1% reply
Recent activity
AI assistant
Draft the whole email from one line.
Describe what the email should do and the assistant writes it in your voice, merge fields and tone already in place. Edit inline, regenerate, or keep what works.
One-line briefs
Tell it the goal; get back a ready-to-send draft with variables filled in.
Tone presets
Friendly, professional, concise, persuasive. Switch and regenerate in a click.
Credits, no surprises
Each draft uses one writing credit, shown before you generate.
app.warmbly.com/campaigns/q1-sales/steps
Sequence
1
Step 1
2
Follow-up
+3d
Add step
Draft saved
Step 1
Compose the email this step sends.
Cold intro
Internal label only. Recipients never see it.
Quick question about Acme's AWS spend, {{.FirstName}}
Edit
Preview
Hi {{.FirstName}}, ...
Hi Alex,
Noticed Acme has been scaling fast on AWS. Teams your size are usually overpaying 30 to 40 percent on compute they spun up once and never tuned.
I help engineering teams find that spend without re-architecting anything. Worth a quick 15-minute call to walk through the three line items I'd check first?
Open to next Tuesday or Wednesday afternoon?
Best,
Jordan
A short intro asking to book a 15-min call about cutting their AWS bill.
DefaultFriendlyProfessionalCasualConcisePersuasive
3 credits remaining
Generated. 2 credits remaining
Integrations
Plug into the stack you already run.
Connect Gmail, Microsoft 365, your CRM, Slack and Zapier over OAuth. Tokens are encrypted at rest and every webhook is HMAC-signed.
OAuth in two clicks
Authorize a provider and Warmbly handles the rest. Revoke anytime.
Signed webhooks
Every event is HMAC-signed and HTTPS by default, with SSRF protection.
Encrypted at rest
Secrets are sealed with your data key, never stored in plaintext.
app.warmbly.com/integrations
Integrations
Connect your stack: CRMs, alerts, automation, meetings, and data
Search integrations
Available
8
providers
Connected
3
3 total
Needs attention
0
all healthy
Meetings
14
booked via integrations
App directory 8
OAuth tokens encrypted at rest. Webhooks HMAC-signed.
G
Gmail
one-click
Send and sync through your Google Workspace mailboxes.
Docs
M
Microsoft 365
one-click
Send and sync through Outlook and Exchange Online mailboxes.
Docs
S
Slack
one-click
Real-time alerts for positive replies, bounces, and deliverability.
Docs
Connect
connected
H
HubSpot
one-click
Push positive replies and new leads straight into your CRM.
Docs
Connect
S
Salesforce
one-click
Sync leads, contacts, and email activity to Salesforce.
Docs
Connect
Z
Zapier
api_key
Triggers and actions across 8,000+ apps.
Docs
Connect
W
Webhooks
webhook
HMAC-signed event delivery to your own endpoint.
Docs
Manage
G
Google Sheets
one-click
On-demand lead sync from a spreadsheet into your contacts.
Docs
Connect
iOS app
The whole workspace, in your pocket.
Replies classified as they land, campaigns you can pause from anywhere, mailbox health at a glance. SwiftUI, in the same open-source repo, on the same realtime socket as the dashboard.
9:41
Positive reply now
[email protected]: Thursday 10am works for me, send over an invite
THURSDAY, JULY 16
Good morning, Mia
2.4K
Sent this week
61%
Open rate
148
Replies
Mailboxes All 12
This week Analytics
Sent Opens
Campaigns See all
Q1 SaaS founders
1,248 sent
41%open 6.2%reply
Berlin startups
312 sent
44%open 7.1%reply
Search in emails
P
L
ALL INBOXES 1.2K 24 unread
JO 3
Jenna Ortiz 9:12
Re: Quick question about Northwind
Thursday 10am works for me, send over an invite and I will get the team in the room.
Interested
MH
Marcus Hale 8:47
Automatic reply: Following up
I am out of the office until Monday with limited access to email.
Out of office
PN
Priya Nair 8:15
Re: Warmbly for agencies
Can you send pricing for around 40 mailboxes? We would move our whole client roster.
Pricing
TB 2
Tom Becker Yesterday
Re: Intro from Sunrise Labs
You: Following up here, any thoughts on the trial?
AS
Ana Silva Yesterday
Re: A quicker way to warm inboxes
Interesting. How does the warmup pool actually work under the hood?
LF
Leo Fischer Tue
Re: Berlin startup outreach
Please remove me from this list.
Unsubscribe
Search campaigns
P
L
ALL CAMPAIGNS 12 6 sending
Q1 SaaS founders 2d
1.2K sent · 486 opens · 78 replies
Running · 50/day
Agency outreach 5d
640 sent · 243 opens · 31 replies
Running · 40/day
Berlin startups 1w
312 sent · 137 opens · 22 replies
Paused · 30/day
Post-demo follow-up 3w
96 sent · 59 opens · 17 replies
Finished · 20/day
Dormant leads revival 4w
No sends yet
Draft · 50/day
Automations
When this happens, do that.
Every reply, booked meeting, bounce and warmup dip is a trigger. Wire it to your stack on a canvas: branch on intent, post to Slack, open the deal, update the CRM. The one below is running its test right now. Press Test in the window to fire it again.
app.warmbly.com/automations/reply-to-revenue
Reply to revenue Active
History Tidy up Saved
Add action Add condition
drag a node's dot to connect · IF block: right dot = yes, bottom dot = no
yes no Prospect replies Trigger
When
campaign.reply_received
if intent is positive · ≥ 80%
S Send a Slack message
Then
#sales · reply from {{.contact_email}}
Create a deal
Then
Discovery · $4,800
H Update HubSpot contact
Then
lifecycle stage · opportunity
Add a tag
Then
nurture
Send a webhook
Then
hooks.yourapp.com/replies
Branches like you think
One IF chip routes on intent, confidence, source, or a random split. Yes goes right, no goes down, and the no path is still yours to wire.
Acts across your stack
Seven built-in actions plus Slack, Discord, HubSpot, Salesforce, Pipedrive, Close and HMAC-signed webhooks. No keys to paste for automation tools.
Test before it is on
Dry-run any automation against a sample event and read every node verdict, yes or no, before the switch ever flips.
Developers
An API you can build a product on.
Everything in the dashboard is a REST endpoint: scoped API keys, idempotent writes, opaque cursors, and HMAC-signed webhooks.
Scoped keys
Mint read, write, or send-only keys per environment and rotate without downtime.
Idempotent by default
Send an Idempotency-Key and retries are always safe.
Webhooks that verify
Subscribe to events like contact.replied with signed payloads.
app.warmbly.com/api-keys
API keys Programmatic access · stripe-style scoped tokens
Search…
Active keys
3
1 inactive
Requests · 24h
8,241
4 errors
Avg latency · 24h
28ms
across all keys
Last call
14s ago
Jun 6, 02:02 PM
Traffic · last 24h 8,241
2xx 4xx 5xx
live; refreshes every minute
Keys 4
production-server Server-side calls from EU production
wmbly_live_a1…4f2a active 600/m
used 2m ago ci-pipeline GitHub Actions deploy step
wmbly_live_7c…91c7 active 120/m
used 1h ago zapier-replies Inbound reply automation
wmbly_live_3d…3d8e active 300/m
used 3d ago old-laptop Rotated out, kept for audit
wmbly_live_0p…xx0p revoked 120/m
used 23d ago Quick start Your first request
curl
Copy
curl https://api.warmbly.com/v1/campaigns \
-H "Authorization: Bearer wmbly_live_a1…" \
-H "Content-Type: application/json"Pass the secret as a Bearer header. Every request returns rate-limit headers (X-RateLimit-Limit, X-RateLimit-Remaining) so well-behaved clients can self-throttle before hitting 429.
Response
200 OK
{
"id": "cmp_01HQX9F7P3A8KY",
"status": "scheduled",
"daily_cap": 50,
"created_at": "2026-06-06T14:02Z"
} HMAC-signed webhooks
Events post to your endpoint with an X-Warmbly-Signature header. Verify the HMAC-SHA256 digest before you trust the body.
contact.replied
delivered 4s ago
CRM
From positive reply to closed won.
When a reply lands positive, Warmbly opens the deal and pauses the sequence on its own. From there you get one timeline that threads every send, open, reply, and stage change back to the exact sequence step that started it.
Born from the reply
A reply classified positive in the unibox opens the deal and pauses the sequence, so nothing keeps sending to someone who already said yes.
One timeline, traced to the send
Every send, open, reply, and stage change lands on the deal, each tagged with the sequence step and mailbox it came from.
Pipeline and forecast in one view
Move deals across your stages on the board while value, weighted total, and probability stay current on the record.
Tasks with a type and an owner
A positive reply spins up a typed follow-up task on the deal, assigned to a teammate with a due date, so the next step never slips.
app.warmbly.com/crm/deals
Deals 8 deals on Sales pipeline
Table
Board
Search deals…
Open
7
active deals
Pipeline value
$140,000
open · all stages
Won
$42,000
closed won
Stages
4
on this pipeline
4 stages 8
live
Qualified 3
$59,700 open
Proposal 2
$39,500 open
Negotiation 2
$40,800 open
Deal DEAL-2026-0184
Stratech
Qualified
Rowan Cole · VP Platform
Value
$45,000
Close
Jul 15
Weighted
$18,000
Probability
40%
Activity
Fields
Tasks
Activity · last 14 days 7 events 8 events
- just nownote Ben Hsu
Logged a call with Rowan. Sending the seat-tiered proposal.
- 2m agoreply Rowan Cole
Replied positively. Classified Positive, sequence auto-paused.
- 2m agostage system
Deal opened in Qualified, linked to the reply.
- 2m agoFollow-up Ben Hsu
Auto-created from the reply, due Jun 10.
- Jun 05note Ben Hsu
Two opens on the Step 02 thread, no reply yet.
- Jun 05send sequence
Step 02 soft follow-up, variant B, from [email protected].
- Jun 04open system
Opened Step 01, tracked near San Francisco.
- Jun 02send sequence
Step 01 initial outreach, variant A, from [email protected].
Changelog
Shipping continuously
The latest from Warmbly.
New features, changes and fixes in the order they reached production. Every entry links to its pull request.
View full changelog
warmbly/warmbly
Apache 2.0
Read the code. Run it yourself.
See exactly how warmup, sending and deliverability work, self-host the whole platform on your own infra, and send a pull request when something should be better.
100%
Open source
$0
To self-host
1
Command to boot
Public
Issues and PRs
warmbly/warmbly
main
Go · Rust · Elixir · TS
cmd/backend API, the control plane Go
cmd/worker Distributed senders Go
tracking Open and click pixels Rust
realtime Live dashboard fanout Elixir
web The dashboard TypeScript
docs docs.warmbly.com MDX
self-host
$ git clone https://github.com/warmbly/warmbly.git
$ cd warmbly && make up
Warmbly is live on http://localhost:8080
$
Self-hosting is free, and you still get the warmup. When Warmbly Cloud launches, link your instance and we warm your mailboxes in the same shared pool the cloud uses: free for up to 10 mailboxes, $15 a month for unlimited. How linking works.
Personalization
One template. A different email for every recipient.
Every step is a template rendered at send time. Merge fields, conditionals, helpers and spintax resolve per recipient, and the composer shows the exact result before you launch.
Step 1 · template written once
{Hi|Hey|Hello} {{.FirstName | default "there"}},
{{if eq .role "Engineer"}}we built this for
teams like yours.{{else}}thought this might
be useful for {{.Company}}.{{end}} Alex Rivera [email protected] · role: Engineer
Hey Alex, we built this for teams like yours.
spintax picked Heyif branch: Engineer
Jenna Carter [email protected] · role: Founder
Hi Jenna, thought this might be useful for Northwind.
else branch{{.Company}}
No first name [email protected] · role: empty
Hello there, thought this might be useful for Brightco.
default "there"blank never breaks
rendered per recipient, at send time
Every field, including yours
Standard fields plus every column from your CSV import. Keys with spaces or dashes work everywhere, even inside conditions.
{{.job title}} Helper functions
Case and string helpers, arithmetic, and numeric compares that coerce strings, so number-like fields just work.
{{if gtf .employees 50}} Spintax, nested
Alternation groups resolve innermost first and nest freely. Subjects spin too, so no two sends read identical.
{Hi|Hey {there|again}} A/B variants per step
Test variants of any step. The original and every variant share the same editor, preview and content score.
Variant B · 50% Previewed with the real engine
The composer renders your template with the actual send engine against sample data. Conditionals, functions and spintax all run.
Hey Alex, Validated before launch
A broken {{if}} blocks the campaign and unresolved tokens get flagged. A failing render falls back to plain substitution, never a lost send.
if: missing {{end}} How we differ
Defaults that protect reputation.
Cold-email platforms typically optimise for volume. Warmbly optimises for sender reputation. The numbers below ship as defaults and the system enforces them.
50, our cap 200+, elsewhere
50 a day per mailbox
The default cap. Raising it takes proof, not a request.
10 minutes apart, always
bursts, elsewhere
Sends are spaced out
600 seconds minimum between two emails from one mailbox.
10%
we quarantine 80%
others react
we quarantine 80%
others react
Acts before it hurts
A mailbox is pulled at 10% spam placement, not 80%.
10 / day 40 / day
Warmup climbs by one
One more email per day. Elsewhere: full volume on day one.
SPF DKIM DMARC
elsewhere: paste DNS records, hope
Verified on connect
A mailbox does not send until its auth records check out.
// constants.go
CampaignLimitDefault = 50
Read the defaults
Every number on this page is open source. Elsewhere: trust us.
One platform
Warmup, sending, inbox, engineered together.
The signal one part collects is the signal the next part acts on.
Inbox 12 unread across 8 mailboxes
Jenna Carter
Re: quick question on outbound
Aman Patel
Re: intro from Maya
Lina Park
Re: pricing tier?
Karim Salah
Re: not the right time
Jenna Carter replied
"Thursday 10am ET works for me."
One inbox
Every reply lands in one place
Replies from all of your sending addresses arrive together, already sorted by what the person actually said.
Warmup healthy
40 / day
up from 10, over 15 days
Runs itself
Mailboxes that warm themselves up
New addresses start slow and build real sending history on their own, so your first campaign is not your first impression.
Step 1
Intro email
replied
Stop here
no more follow-ups
no reply
Wait 3 days
business hours
Step 2
Follow-up
Knows when to stop
Follow-ups that end at "yes"
Each step branches on what the person did. Answer once and the rest of the sequence is cancelled automatically.
By provider
Gmail 97%
Outlook 95%
Yahoo 94%
96%
reached the inbox
No guessing
See if you landed in the inbox
We test where your mail actually arrives at each provider, so you find out before your reply rate does.
Compose 1 of 2,480
Hi {{first_name}}Jenna,
Saw {{company}}Northwind is hiring across {{team}}support. We keep outreach out of the spam folder for teams that size.
Worth a look?
Sounds human
Written once, personal to everyone
Pull real details from your contact list so each person gets their own version, without writing each one.
Pricing
Pay for what you send.
The number on each card is daily send volume. Warmup, the unified inbox, analytics, CRM and the API are in every paid plan.
Starter
Great for small businesses with a small budget.
$23 $29
/ month · billed yearly
Save $72 a year
150 sends / day
- Unlimited warmup
- Unlimited mailboxes
- Unified inbox with reply detection
- Sequences that stop on reply
- Inbox placement monitoring
Grow
Ideal for growing businesses scaling their outreach.
$71 $89
/ month · billed yearly
Save $216 a year
3,000 sends / day
- Everything in Starter
- CRM with pipelines and deals
- A/B variants per step
- Bulk contact import
- API and signed webhooks
Business
Most popularFor established teams that need higher limits and advanced features.
$263 $329
/ month · billed yearly
Save $792 a year
15,000 sends / day
- Everything in Grow
- Sending kept apart from other customers
- Team roles and permissions
- Full audit log
- Priority support
Enterprise
Large orgs with custom volume and dedicated support.
Custom
/ month · billed yearly
15,000+ sends / day
- Everything in Business
- Custom volume and contract
- BYOK encryption · SSO / SAML
- Custom data residency
- Dedicated CSM
All plans include warmup, sending, inbox, analytics and CRM.
See full comparison
Self-hosting is free. When Warmbly Cloud launches, link your instance and we warm up to 10 of your mailboxes in the shared pool at no cost, unlimited for $15 a month.
Send cold email people actually open.
Connect a mailbox, warm it up, send your first campaign today.