Sending Interval Between Emails (Per Mailbox, Not Global)
The 'Minutes Between Sends' setting on a campaign controls how long each individual mailbox waits between its own consecutive sends. It is enforced per mailbox, not globally across the campaign.
What 'Per Mailbox' Means
Each mailbox assigned to the campaign enforces the interval independently. If you set a 5-minute interval and have multiple mailboxes assigned, all of them send in parallel — they do not queue behind one another. Each mailbox simply waits 5 minutes between its own sends.
Worked Example
Configuration: 5-minute interval, sending window 7 AM – 5 PM (10 hours = 600 minutes), 5 mailboxes assigned, daily send limit 1000.
• Each mailbox can send up to 600 / 5 = 120 emails per day.
• Across 5 mailboxes running in parallel, the campaign can send up to ~600 emails per day.
• The actual number sent is the lowest of: campaign daily send limit, sum of per-mailbox daily caps, and (per-mailbox interval cap × number of active mailboxes).
Why It Is Per Mailbox, Not Global
The interval exists to protect mailbox reputation — sending too fast from a single inbox is what triggers spam filters. Different mailboxes are independent inboxes with their own reputations, so there is no deliverability reason to make them wait on one another. Per-mailbox pacing gives you proportionally higher throughput when you add more mailboxes, while keeping every individual mailbox safe.
Cross-Campaign Pacing on Shared Mailboxes
If the same mailbox is assigned to two different campaigns, the interval is still honored on that mailbox — campaign A and campaign B cannot fire seconds apart through the same inbox. The system tracks the last send timestamp per mailbox across all campaigns and warmup, so the gap is enforced globally for that inbox even when multiple campaigns share it.
Recommended Values
• Established domains and mailboxes: 1–3 minutes is typically safe.
• Newer domains or mailboxes still in early ramp: 5–10 minutes is recommended.
• Maximum allowed: 60 minutes.
Daily Capacity Estimate (UI Note)
The 'Daily Capacity Estimate' shown inside the campaign wizard is conservative and treats the interval as if it applied across the whole campaign. The actual backend behavior is per-mailbox, so when multiple mailboxes are assigned the real sending capacity is higher than the wizard estimate suggests. The authoritative ceilings are the campaign daily send limit, the per-mailbox daily cap, and the per-mailbox rate limits — not the wizard's estimate.
Key Takeaway
More mailboxes at the same interval = proportionally more total throughput. The interval setting is about pacing each individual inbox safely, not about throttling the campaign as a whole.