Sending limits are the throttles that set how many emails each mailbox, campaign and workspace may send per day, how fast volume ramps, and how far apart messages go out. Buyers care because breaking them burns domains, and because the monthly email allowance tied to these limits is how most volume tools price.
How it works
There are four layers. Most tools expose all of them.
- Per-mailbox daily cap. The consensus for cold mailboxes is about 30 a day. Instantly recommends 30 campaign emails a day per account, 20 for its AirMail mailboxes. lemlist says 30–40 for new mailboxes, and under 70 a day per provider including warm-up and manual email.
- Per-campaign daily cap. Instantly's rule of thumb is accounts × 30. Smartlead's API also exposes a daily sending cap and "what % of leads get follow-ups", which splits daily capacity between new leads and follow-ups.
- Ramp. Instantly's slow ramp adds 2 campaign emails a day until the cap is reached.
- Gap / jitter. Instantly defaults to a 1-minute minimum gap when a mailbox is shared across campaigns. Smartlead describes "reactive sending algorithms that emulate 'human' sending patterns".
Warm-up traffic does not count toward Instantly's limits. lemlist counts it toward its per-provider ceiling. That difference matters: 30 cold emails plus 40 warm-up emails is a 70-a-day mailbox as far as Google is concerned.
Who does it well
Per-mailbox defaults compared, from a 2026 table on the blog of data vendor Prospeo (Prospeo, 2026). It is a competitor-adjacent source, so treat it as indicative:
| Tool | Daily per-mailbox figure | Nature |
|---|---|---|
| Instantly | 30 recommended | Vendor help centre confirms |
| lemlist | 30–40 for new mailboxes | Vendor help centre confirms |
| Smartlead | ~30 | Prospeo |
| Apollo | 50 recommended | Prospeo |
| Woodpecker | ~50 | Prospeo |
| Reply.io | ~50–100 | Prospeo |
| HubSpot Pro / Enterprise | 500 / 1,000 hard cap | Prospeo; HubSpot KB not verified |
| Outreach | 5,000 per week per mailbox | Prospeo |
The HubSpot and Outreach caps come only from Prospeo's table. The HubSpot knowledge-base page on limits could not be loaded in this pass.
Monthly allowances are the commercial side of limits (as of October 2026):
| Tool | Entry | Volume tier |
|---|---|---|
| Instantly | 5,000 emails, $47 | 500,000 emails, $358 (pricing) |
| Smartlead | 6,000 emails, $39 | 500,000 emails, $379 (pricing) |
| EmailBison | n/a | 500,000 emails, $599 (pricing) |
| PlusVibe | 25,000 emails, from $37 | 500,000+, from $497 (pricing) |
| Salesforge | 5,000 emails, $40 | 50,000 emails, $80 (pricing) |
| Saleshandy | 6,000 emails, $41/mo monthly | Unlimited on Scale, $189/mo monthly (pricing) |
Where implementations differ
- Static vs adaptive. Almost every tool uses a static number that the user sets. PlusVibe is the documented exception. Its account automations cut campaign and warm-up limits when 3-day bounce rate, 7-day warm-up health or reply rate cross a threshold, then restore them after a recovery period. Instantly's Deliverability AI Agent can pause campaigns and replace accounts, on Hyper Growth and up.
- Company-level throttles. Instantly can limit emails per company domain per day. Smartlead's company-level auto-pause stops messaging an organisation after one reply. Both protect against hitting one corporate gateway 40 times in an hour.
- Recipient-provider limits. lemlist frames its cap per provider. Most others frame it per mailbox only.
- Sending windows and time zones are universal. Their quality varies, but they no longer decide a sale.
Risks and abuse
Limits are the vendor's main lever for keeping customers inside provider tolerances, and the main thing customers try to get around. Rotation (Inbox rotation) multiplies them across domains. Vendors that sell infrastructure have a commercial reason to set low per-mailbox defaults, because each customer then needs more mailboxes (Google vs Microsoft vs SMTP, Infrastructure strategy: build or partner). Google publishes hard technical send caps for Workspace and Microsoft has its own, but cold-email reputation fails long before those are reached. See Microsoft rules: Outlook.com and Microsoft 365 limits and Volume math: what 10k and 100k emails a day cost.
The ~30/day default is folklore that has hardened into a norm. No vendor publishes evidence for it. A tool that sets limits per mailbox from observed placement and reply data, rather than a constant, would have a real, explainable edge.
What this means for an entrant
- Ship all four layers (mailbox, campaign, ramp, jitter) plus per-company-domain throttles at launch.
- Count warm-up toward the mailbox's real daily total, or at least show it. Mailbox providers see total volume, not "campaign" volume.
- Make limits adaptive: lower a mailbox's cap on bounce, complaint or placement drops, and step it back up. PlusVibe proves buyers will configure this, and the bigger players have not made it the default.
- Price on emails sent or contacts, not mailboxes. That keeps the incentive to inflate mailbox counts away from your pricing (Pricing strategy).
- Expose the actual send log (time, mailbox, recipient provider). Agencies debugging deliverability want the raw data, not a dashboard.