When it comes to sending reminders for follow-ups, approvals, and payments, channel choice matters more than most people realize. The wrong channel can mean the difference between a same-day response and a week of silence.
We analyzed response patterns across thousands of reminders sent through autoremind.ai to bring you definitive data on this question.
The Short Answer
For internal teams: Slack wins - 3x faster average response time.
For external clients/vendors: Email wins - more professional, creates a paper trail, and clients check it more.
But the nuance matters. Let's break it down.
Response Time Comparison
| Scenario | Slack Avg Response | Email Avg Response |
|---|---|---|
| Internal team member | 47 minutes | 2.8 hours |
| Colleague in same company | 1.2 hours | 4.1 hours |
| External client | 6.3 hours | 5.1 hours |
| Vendor/supplier | 8.2 hours | 6.4 hours |
The pattern is clear: Slack outperforms email for internal communication, but email edge out Slack for external stakeholders.
Why Slack Wins Internally
Lower friction
Slack feels conversational. Replies are short, fast, and don't require formality. A quick "On it!" is enough.
Presence indicators
You can see when someone is online. Timing a follow-up when someone is active dramatically increases immediate response rates.
Channel context
In Slack, reminders in a project channel are visible to the whole team, creating gentle social accountability.
Why Email Wins Externally
Professionalism signal
Email still carries more professional weight for business transactions, particularly payments and formal approvals.
Client habits
Most clients check email more reliably than any other communication tool - it's universal.
Documentation
Email creates a clean paper trail that's valuable for disputes, audits, and compliance.
Use Cases: Which Channel to Choose
Use Slack for:
- Internal project deadlines
- Team task approvals
- Stand-up reminders
- Cross-functional coordination
- Anything time-sensitive with internal stakeholders
Use Email for:
- Invoice reminders
- Client follow-ups
- External vendor communications
- Formal notices
- Legal or compliance-related follow-ups
The Hybrid Approach
The most effective teams use both strategically. Here's the pattern that gets the best results:
- Initial outreach: Email (formal record)
- First follow-up: Email (same thread)
- Second follow-up: Slack DM if available ("Hey, did you see my email about X?")
- Third follow-up: Email with urgency escalation
This hybrid approach combines email's professionalism with Slack's immediacy.
Setting Up Multi-Channel Reminders in autoremind.ai
autoremind.ai lets you set up reminders across both channels. You can:
- Send follow-ups via email for external clients
- Mirror internal status updates to Slack
- Escalate from email to Slack after no response
Just describe it naturally: "Follow up with the design team on Slack about the homepage mockups every 2 days. Also email the client every 3 days about the project approval."
Conclusion
There's no one-size-fits-all answer - and that's exactly the point. The best channel is the one your recipient uses most.
For remote-first teams, that's Slack. For external business relationships, that's email. The best reminder systems use both.
The important thing is to actually send the reminders. Most people don't follow up consistently enough — and that's the single biggest factor in whether you get responses.