Daily sending limits: mailbox limit vs campaign limit
Two separate limits decide how many emails go out each day, and confusing them is the most common reason a campaign sends less (or more) than expected. The mailbox limit caps what one mailbox sends…
Draft — written from product facts + domain knowledge; UI labels to be verified before publishing.
Two separate limits decide how many emails go out each day, and confusing them is the most common reason a campaign sends less (or more) than expected. The mailbox limit caps what one mailbox sends across all campaigns. The campaign limit caps how many new leads one campaign starts. Both must allow a send for it to happen.
The two limits
| **Mailbox limit** | **Campaign limit** | |
| Where | **Mailbox** page → select mailboxes → bulk action **campaign emails per day** (or per-mailbox settings) | Campaign → **Edit Campaign** → **Settings** → **Daily new contacts limit** |
| Scope | One mailbox, all campaigns combined | One campaign, all its mailboxes combined |
| Counts | Every campaign email (step 1 and follow-ups). Warm-up emails are separate. | Only first emails to new leads |
| Protects | Mailbox reputation | Pace of a campaign |
How they combine
Each time a send is due, OutreachFox checks:
- Is the campaign inside its sending schedule window? If not, wait.
- Is this a new lead, and has the campaign already reached its Daily new contacts limit today? If so, wait until tomorrow.
- Is there a mailbox attached to the campaign that still has room under its own daily limit? If not, wait.
Daily capacity of a campaign is therefore the sum of the free capacity of its mailboxes, and part of that goes to follow-ups, which the campaign limit does not count.
Steps: set the mailbox limit
- Click Mailbox in the left navigation.
- Tick the mailboxes to change.
- From the bulk actions, choose the option to set campaign emails per day and enter the number.
- Save.
Steps: set the campaign limit
- Open the campaign → Edit Campaign → Settings.
- Set Daily new contacts limit.
- Save, then Resume Campaign.
Recommended numbers
- Mailbox limit: 30–50 campaign emails per day for a mailbox that has warmed for 2–3 weeks; 10–20 during the first week of sending. Never above 50 for cold outreach, even on old mailboxes.
- Campaign limit: about half of the combined mailbox capacity, so follow-ups always have room.
Example: 8 mailboxes × 40 = 320 emails/day of capacity. Campaign limit 150 new leads/day. A 3-step sequence over 10 days then settles at roughly 150 first emails + 150–170 follow-ups per day, inside capacity.
Tips
- Sharing mailboxes between campaigns divides their capacity between the campaigns. Prefer a dedicated mailbox pool per campaign when you can.
- Raise mailbox limits gradually (5–10 per day per week). A jump from 20 to 50 overnight looks like a compromised account to the provider.
- Warm-up emails use a separate allowance managed by the warm-up profile and do not count toward the campaign limit.
Troubleshooting
- Campaign sends far fewer than the campaign limit: mailbox limits are the bottleneck. Check the combined capacity of the attached mailboxes.
- A mailbox stopped sending mid-day: it reached its daily limit; sending resumes tomorrow. If it stopped with an error, check its connection under Mailbox.
- Follow-ups are late: total capacity is too low for the number of leads in the sequence. Add mailboxes or lower the daily new-contacts limit.
Related articles
- Set the daily new-contacts limit for a campaign
- Choose a sending strategy: follow-ups first, balanced, or new leads first
- Inbox rotation: how OutreachFox spreads sends across mailboxes
- Bulk mailbox settings
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