Safe sending limits
Each inbox should send only a small number of cold emails a day. To send more, you add more inboxes, not more emails per inbox. This is the most important rule in cold email infrastructure, and it’s why plans come with many inboxes rather than a few busy ones.
Safe daily sends per inbox
Section titled “Safe daily sends per inbox”| Inbox type | Safe cold emails per inbox per day |
|---|---|
| Outlook (normal) | 10 |
| Outlook Premium | 12 |
| Google Workspace | about 20 |
| SMTP | 8 |
These are safe limits, not targets. Staying a little under them is fine. Going over them regularly is how inboxes get flagged, throttled or suspended. Warmup emails don’t count towards these numbers; they run on top.
Why spread the volume
Section titled “Why spread the volume”Email providers watch for patterns that look like bulk mail. One inbox sending 200 emails a day looks like a machine. Twenty inboxes sending 10 each looks like twenty people doing their normal work. Spreading volume also limits the damage when something goes wrong: if one inbox or domain has a bad day, the rest keep sending.
Your sequencer handles the spreading for you. It rotates sends across all connected inboxes and paces them through the day, so check that each inbox’s daily limit in the sequencer matches the table above.
A few habits help:
- Spread sends across the day. Don’t send everything at 9am.
- Vary the daily volume a little rather than sending exactly the same number every day. The Cold Email Bible suggests letting it move up or down by about 15 to 25%.
- Mix inbox types. The Diversified plans combine Outlook, Google and SMTP, so a change at one provider doesn’t stop all your sending.
Keep a reserve
Section titled “Keep a reserve”Domains wear out over time when they’re used for cold email, so it’s normal to retire some and bring in replacements. Don’t plan to run every inbox at its full limit every day. Keep some capacity spare so you can rest or swap a domain without your volume dropping.
How much? Our help articles suggest keeping 10 to 20% spare capacity. The Cold Email Bible is more cautious and keeps half of all capacity as a warm reserve. Starting out, somewhere in that range is a sensible rule of thumb.
Worked example: how much can you send?
Section titled “Worked example: how much can you send?”Say you want about 50 booked calls a month. Using our rule of thumb (about 1 booked call per 500 cold emails), that’s 25,000 emails a month.
Cold email usually goes out on working days only. With about 20 sending days a month:
25,000 emails ÷ 20 days = 1,250 emails a day
Add a 20% reserve and you want room for about 1,500 emails a day. Here’s what that takes with each inbox type on its own:
| Inbox type | Safe per inbox per day | Inboxes for 1,500 a day | Domains |
|---|---|---|---|
| Outlook Premium | 12 | 125 | 2 (up to 100 mailboxes per tenant) |
| Outlook (normal) | 10 | 150 | 2 |
| Google Workspace | about 20 | 75 | 15 (5 inboxes per domain) |
| SMTP | 8 | 188 | 38 (5 inboxes per domain) |
In practice you’d mix types rather than pick one, which is what the Diversified plans do. For 25,000 emails a month, the plan rule of thumb points to Diversified Starter (up to 40,000 sends a month), which already leaves room to spare.
When to stop sending from an inbox
Section titled “When to stop sending from an inbox”Pause an inbox (and message the team) if you see any of these:
- bounces above 5% of what it sends,
- several spam complaints from the same domain,
- it suddenly starts landing in spam,
- Microsoft or Google sends a throttling or suspension notice.
Pausing early often saves the domain. See Common errors for what each sign means.