Connect Instantly to your Inboxlee mailboxes in 60 seconds
API-key sync, sending limits, daily caps. Step-by-step with screenshots-grade detail.
Rejwan Nirob·Feb 5, 2026·4 min readInstantly is one of the three sending tools Inboxlee integrates natively. Connecting takes one API key and roughly a minute of your time. Here is the full process.
Step 1 - Generate an Inboxlee API key
In your Inboxlee workspace, go to Settings → API keys. Click Create new key, name it "Instantly sync", grant mailboxes:read scope, and copy the key. It is shown once - paste it somewhere safe.
Step 2 - Connect in Inboxlee Integrations
In Inboxlee dashboard go to Integrations → Instantly. Click Connect. Paste your Instantly API key (found in your Instantly dashboard under Settings → API). Click Save. Inboxlee immediately syncs all live mailboxes into Instantly.
Step 3 - Verify and configure limits
- Open each mailbox in Instantly → Email Accounts
- Confirm the daily send limit matches your warmup stage (5 to 20 ramp during days 1 to 14)
- After day 14, cap at 10 to 20 per day per mailbox for cold outbound - well below the platform ceiling
- Verify the warmup toggle is on - Instantly handles warmup, Inboxlee tracks the curve
Inboxlee reads warmup-day, daily volume, and curve from your Instantly account via the same API key. Your sender warms - Inboxlee surfaces the data.
Connect InstantlyFrequently asked
How do I connect Instantly to my Inboxlee mailboxes?
Generate an Inboxlee API key (Settings → API keys, mailboxes:read scope), then paste it in Inboxlee → Integrations → Instantly → Connect along with your Instantly API key. All live mailboxes sync to Instantly within seconds. CSV bulk-import is also available as a fallback.
What daily-send cap should I use in Instantly for cold email?
10 to 20 emails per mailbox per day for safe cold outbound, after the 14-day warmup ramp. Instantly will let you set higher, and Workspace/M365 will technically tolerate up to ~500/day at full reputation, but sustained sends above 20/day correlate with placement decline in partner-program telemetry.
Does Instantly run mailbox warmup automatically?
Yes. Instantly has its own warmup network - inbox-to-inbox synthetic engagement during the 14-day ramp. Enable the warmup toggle on each connected mailbox. Inboxlee reads the warmup-day, daily volume, and engagement curve back from the Instantly API so you see everything in one dashboard.
How long does Instantly warmup take?
14 days minimum before sending real cold campaigns. During warmup, Instantly sends a few messages per day to its warmup network, those messages are auto-opened and auto-replied to build engagement signals. Inboxlee tracks the curve and surfaces a warning if the ramp is too aggressive.