How to Configure Smartlead Campaign Settings for ColdSend Inboxes

ColdSend inboxes are powered by Azure Communication Services (ACS), which enforces a hard limit of 100 emails per hour per domain. This limit is shared across every platform sending from that domain — including ColdSend itself.

If you exceed this limit, emails are hard rejected (not queued). This guide shows you exactly what values to set in Smartlead's campaign settings to stay within the quota.

Prerequisite: This guide assumes you've already connected your ColdSend inboxes in Smartlead. If you haven't, follow this guide first: How to Export Inboxes from ColdSend and Connect Them in Smartlead

Understand the Domain Quota

Before setting your campaign values, you need to understand three things:

1. The limit is per domain, not per inbox. Whether you have 1 inbox or 100 on the same domain, the combined sending across all of them cannot exceed 100 emails per hour.
2. The limit is shared across platforms. If ColdSend is also sending emails (campaigns, warmup) on the same domain, those emails count toward the same 100/hour pool.
3. Exceeding the limit causes hard rejections. Emails that go over the quota are not queued or retried — they simply fail.

Smartlead Controls Explained

Smartlead uses three controls that affect your sending rate:

The Every setting is the primary rate control. Combined with the sending window, it determines your daily volume automatically — there is no separate "daily limit" field.

Smartlead automatically adds 30–60 seconds of random variance to each send for natural sending patterns. This is built in and doesn't affect your quota calculations.

Which Case Applies to You?

Choose the case that matches your setup:

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Case A: Smartlead Only

Use this case when your ColdSend inboxes are connected in Smartlead but you are not actively sending campaigns or running warmup from ColdSend on the same domain.

Your full domain quota of 100 emails/hour is available for Smartlead.

The Formula

Every (minutes) = (Number of active inboxes × 60) ÷ 100   ← round UP

Quick Reference Table

How to Apply

1. Count how many inboxes from the same domain are active in your Smartlead campaign.
2. Find the matching row in the table above.
3. In Smartlead, open your campaign Settings and set:
   • From / To — your desired sending window (e.g., 09:00 to 18:00)
   • Every — use the value from the table
4. If your inbox count falls between two rows, use the higher interval (more conservative).

Smartlead Sending Window Settings

Setting New Leads/Day

New Leads/Day controls how many new contacts each inbox reaches out to per day. Since follow-ups also count toward sending volume, set this conservatively:

• If most of your leads are new (first email), you can set this close to the "Sends per inbox per day" value from the table.
• If many leads are in follow-up sequences, set New Leads/Day lower — follow-up emails consume the same quota as first touches.

Rule of thumb: If you have active follow-up steps in your sequence, set New Leads/Day to roughly half the daily sends per inbox to leave room for follow-up volume.

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Case B: ColdSend + Smartlead

Use this case when you're actively running campaigns or warmup in ColdSend and sending from Smartlead on the same domain.

Your domain quota of 100 emails/hour must be split between ColdSend and Smartlead.

Step 1: Estimate ColdSend's Hourly Usage

Check how many emails per hour ColdSend is sending on the domain. This includes:

• Active campaigns — check your campaign's sending rate in ColdSend
• Warmup emails — each inbox in warmup sends a small number of emails per hour

Tip: A rough estimate is fine. If you have 20 inboxes in warmup with a warmup limit of 2/day each, that's roughly 40 emails spread across the day — about 2–3 per hour. Active campaigns are easier to estimate from the daily limit divided by sending hours.

Let's call this number S (ColdSend emails per hour).

Step 2: Calculate Your Remaining Budget

Remaining budget (R) = 100 − S

Example: If ColdSend is sending ~20 emails/hour, your remaining budget for Smartlead is 80 emails/hour.

Step 3: Apply the Formula

Every (minutes) = (Number of active inboxes × 60) ÷ R   ← round UP

Quick Reference Tables

If ColdSend uses ~20 emails/hour (R = 80):

If ColdSend uses ~40 emails/hour (R = 60):

If ColdSend uses ~60 emails/hour (R = 40):

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General Formula (Custom Values)

If your setup doesn't match the tables above, use this formula directly:

Inputs:

• N = number of inboxes from the domain active in Smartlead
• S = emails per hour ColdSend is sending on the same domain (0 if not using ColdSend)
• R = 100 − S (remaining hourly budget for Smartlead)
• H = sending window in hours (e.g., 09:00–18:00 = 9 hours)

Outputs:

• Every (minutes) = (N × 60) ÷ R ← round UP
• Estimated sends per inbox per day = (H × 60) ÷ Every

Important: Always round the interval up to stay safely under the quota.

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Setting Values in Smartlead

1. Open your campaign in Smartlead.
2. Go to Settings.
3. Find the Sending Window section:
   • From — set the start time (e.g., 09:00)
   • To — set the end time (e.g., 18:00)
   • Every — set the interval in minutes from the tables or formula above
4. Set New Leads/Day based on the guidance above.
5. Save your settings.

If you're running multiple campaigns using the same domain's inboxes, the combined volume across all campaigns counts toward the domain quota. Make sure the total doesn't exceed R.

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Common Mistakes to Avoid

Setting a Low Interval Without Counting Inboxes

The most common mistake is setting "Every 5 minutes" on every inbox, assuming each has its own limit. With 100 inboxes on a domain, a 5-minute interval would attempt ~1,200 emails per hour — far above the 100/hour limit.

Forgetting ColdSend's Own Sending

If ColdSend is actively sending campaigns or warmup on the same domain, those emails count. Ignoring this will cause rejections even if your Smartlead settings look correct on their own.

Running Multiple Smartlead Campaigns on the Same Domain

If you have two or more Smartlead campaigns using inboxes from the same domain, each campaign draws from the same 100/hour pool. Add up the hourly throughput of all campaigns and make sure the total stays under R.

Ignoring Follow-Up Volume When Setting New Leads/Day

Follow-up emails consume the same domain quota as first-touch emails. If you set New Leads/Day too high and your sequence has multiple follow-up steps, the combined volume (new + follow-ups) can exceed what the interval allows.

Not Adjusting When Adding More Inboxes

If you add more inboxes to your campaign later, you must increase the interval accordingly. The quota doesn't grow with more inboxes — it's fixed per domain.

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Troubleshooting

Emails Are Being Hard Rejected

• Verify your "Every" interval matches the formulas above
• Check if ColdSend is sending more than you estimated — look at your ColdSend campaign stats for the domain
• Count the actual number of active inboxes on the domain in Smartlead (some may have been added to campaigns without your noticing)

Sending Feels Too Slow

This is expected with a shared domain quota. To increase throughput:

• Use more domains — spread your inboxes across multiple sending domains, each with its own 100/hour quota
• Reduce ColdSend's usage — pause warmup or lower campaign volume in ColdSend to free up budget for Smartlead
• Run fewer inboxes at a time — use a subset of your inboxes in Smartlead and rotate them

Some Inboxes Send Fine but Others Don't

• Check if all inboxes are on the same domain — if some are on different domains, they have separate quotas
• Verify no inbox has been disconnected or has invalid credentials in Smartlead

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FAQs

What happens if I set the interval too low?
Your domain will exceed the 100 emails/hour limit and ACS will hard reject the excess emails. These emails are not retried — they're lost. Always err on the side of a higher interval.

Can I use all 100 inboxes from my domain in Smartlead?
Yes, but each inbox will only send about 1 email per hour (or less if ColdSend is also sending). This works for large lead lists where you don't need high throughput per inbox.

Does warmup in Smartlead count toward the domain limit?
Yes. Any email sent through the inbox — whether it's a campaign email, a warmup email, or a follow-up — counts toward the 100/hour domain quota. If Smartlead's warmup is running alongside campaigns, factor that into your calculations.

Do follow-up emails count toward the quota?
Yes. Every email sent from the inbox counts — first touches, follow-ups, and replies sent through sequences. This is why New Leads/Day should be set conservatively when your sequences include follow-up steps.

How do I know how many emails ColdSend is sending per hour?
Check your ColdSend campaign settings for the daily limit and sending window. Divide the daily limit by the number of sending hours to get the hourly rate. Add any warmup volume on top.

Can I run campaigns on ColdSend and Smartlead at the same time?
Yes, as long as the combined hourly volume across both platforms stays under 100 emails per domain. Use Case B above to calculate the correct split.

What if I have inboxes on multiple domains?
Each domain has its own independent 100/hour quota. Apply the formula separately for each domain.