ColdStack
Sends positive cold email replies from Instantly, Smartlead and EmailBison into Slack so you can answer leads without leaving Slack.
From $49/mo 14-day free trial
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Bottom line
ColdStack is a Slack app that routes positive cold email replies from Instantly, Smartlead and EmailBison into Slack and lets you answer them there. It suits recruiters and small agencies whose team already lives in Slack and wants hot leads in front of them fast. Plans start at $49 a month at the current launch price, with a 14-day free trial and no card required.
Stands out for: It keeps the whole reply loop inside Slack, so a recruiter can answer an interested hiring manager from the Slack mobile app without opening Instantly or Smartlead. That is a far lighter and cheaper setup than a full reply platform such as Master Inbox, which starts at $599 a month.
Watch out for: It covers three sequencers only, Instantly, Smartlead and EmailBison, and LinkedIn replies are not mentioned. Current prices are a 50% launch discount for the first 2,000 users, so the regular rates of $79 and $259 a month may apply later, and the Agency plan holds only three client spots.
Overview
ColdStack connects your Instantly, Smartlead or EmailBison accounts to Slack. Once linked, positive replies from your campaigns appear in a dedicated Slack channel, and replying in Slack sends the response straight to the lead from the original sending platform.
For a recruiting desk doing business development, that means the person on shift sees an interested reply the moment it lands, including on the Slack mobile app, and answers it without switching tools. Every plan includes unlimited team members and real-time notifications.
The Solo plan adds CRM connections, naming HubSpot, Attio and GoHighLevel, with positive replies added to the CRM automatically. The Agency plan adds up to three client spots, a custom domain, a custom Slackbot name and logo and an agency view for managing clients and reply stats.
Who it's for
Best for
- Recruiters whose desk already runs in Slack
- Small agencies on Instantly, Smartlead or EmailBison
- Teams that want positive replies flagged fast on mobile
- Agencies wanting a white-labeled Slackbot for clients
Not ideal for
- Teams that also need LinkedIn replies handled
- Agencies with more than three clients on one plan
- Teams on sequencers other than the three supported
Key features
Replies in Slack. Positive replies from Instantly, Smartlead and EmailBison campaigns flow automatically into a dedicated Slack channel.
Reply from Slack. Click reply in Slack and the response goes straight to the lead, with no need to log into each sending platform.
Smart reply filtering. Only positive replies are pushed to the channel, so the team sees the leads worth answering first.
CRM hand-off. The Solo plan lists connections to HubSpot, Attio and GoHighLevel and automatic adding of positive replies to the CRM.
White label for agencies. The Agency plan adds a custom domain, a custom Slackbot name and logo and an agency view of reply stats per client.
Pricing
| Plan | Price | What you get |
|---|---|---|
| Solo | $49/mo | Launch price, regular $79/mo; unified Slack inbox, CRM sync |
| Agency | $129/mo | Launch price, regular $259/mo; 3 client spots, white label |
ColdStack has two plans, both with unlimited team members and real-time notifications. Solo is $49 a month, shown as a 50% launch discount from $79 for the first 2,000 users, and covers the unified Slack inbox for Instantly, Smartlead and EmailBison, direct replies from Slack, CRM connections and automatic adding of positive replies to the CRM. Agency is $129 a month, discounted from $259, and adds up to three client spots, a custom domain, a custom Slackbot name and logo, a full white-label experience and an agency view of client reply stats. Both plans include a 14-day free trial with no credit card required. Confirm current terms on the vendor site.
Checked 4 Nov 2026. Vendors change prices without notice.
Is ColdStack expensive?
ColdStack starts at $49/mo. We list 144 outreach tools in total. 30 have a free tier, and those with a public price typically start around $49 a month.
- 22 quote-based
- 30 free tier
- 122 public price
Worked out automatically from every outreach listing, so it updates as the directory changes.
Pros and cons
Pros
- Low entry price for a reply tool
- Answer leads without leaving Slack
- 14-day trial with no card
Cons
- Three sequencers supported
- Launch discount pricing
- Agency plan capped at three clients
Integrations
Instantly Smartlead EmailBison Slack HubSpot Attio GoHighLevel
What's new at ColdStack
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How ColdStack compares
See all ColdStack alternatives, with what each one does differently and a head to head for every pairing.
| Tool | Free tier | From | MCP | API | Compare |
|---|---|---|---|---|---|
| | – | $49/mo | – | – | |
| | – | $599/mo | – | ✓ | Compare |
| | – | $99/mo | – | ✓ | Compare |
| | – | $37.60/mo | ✓ | ✓ | Compare |
$599/mo API
EmailBison's own inbox handles replies inside the sequencer, while ColdStack pushes positives from EmailBison, Instantly and Smartlead into one Slack channel.
$99/mo API
OutboundSync focuses on syncing sequencer replies into the CRM, while ColdStack puts them in Slack for a fast human reply.
$37.60/mo MCP API
Instantly's own unibox and Slack alerts may be enough if you only send from Instantly and do not need to reply from Slack.
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