---
title: "Inboxes for Instantly: Setup, Limits and Deliverability"
description: "Run WarmInboxes Google, Microsoft 365 and Azure mailboxes in Instantly: connecting them, the safe daily limit per platform, warmup, and fixing a flagged inbox."
url: https://warminboxes.com/instantly-inboxes
breadcrumb: "Home > Inboxes for Instantly"
---
# Inboxes for Instantly

14 October 2026 · @Huz

Official Google Workspace, Microsoft 365 and Azure mailboxes, built and authenticated by us and plugged into your Instantly workspace. This is what to connect, what daily limit to set on each inbox, and what to do when one starts slipping mid-campaign.

WarmInboxes is [Instantly Certified Expert](https://instantly.ai/experts/huzaifa-majeed).

“I made every single deliverability tool our agency GTMEs deploy to get 5%+ avg reply rate public and free.”

Huz 🧡

Connect with me

## Before you connect anything

Most of the trouble people have connecting mailboxes to Instantly is not in Instantly. It is a mailbox that is not finished, and the sequencer is simply the first thing that notices. Four things want to be true before you open the Email Accounts screen:

- **The mailbox exists and you own the admin.** Every inbox we deliver is a real Google Workspace, Microsoft 365 or Azure mailbox on a licensed tenant, not a relay or an alias. You get the admin, so you can rotate a password or revoke a token without asking us.
- **DNS is already published.** SPF, DKIM, DMARC and forwarding are configured before handover. You do not have to add records, but it is worth confirming rather than assuming — run the domain through the [deliverability grader](https://warminboxes.com/deliverability-checker), which does SPF, DKIM, DMARC, MX, blacklists and domain age in one pass.
- **Two-factor is settled.** On the day of delivery, either disable 2FA on the receiving account before we hand over, or keep it locked down and give restricted sub-account access to support@warminboxes.com. Orders where 2FA is still on and no access was granted take longer than the usual 48 to 72 hours.
- **You know which connection method you are using.** OAuth for Google and Microsoft, or IMAP and SMTP for anything else. Which one matters more than it looks, and the next section is about why.

## Connecting the inboxes

Instantly moves its menus around, so these steps are written as what you are doing rather than as a click path that will be wrong by next quarter. The shape has been stable for years even when the labels have not.

- 1**Add the accounts by provider, not generically.** Instantly offers a Google option, a Microsoft option and a generic IMAP/SMTP option. Use the matching provider path for Google Workspace and Microsoft 365 inboxes. It authorises over OAuth, which means no password is stored, nothing breaks when a password is rotated, and you skip the app-password dance entirely.
- 2**Use the bulk upload once you are past a handful.** Connecting forty mailboxes one at a time is an afternoon. Instantly takes a CSV of accounts, and we hand over credentials in a form you can shape into one. If you have asked us to connect them for you, this is the part we are doing.
- 3**Expect SMTP AUTH to be off on new Microsoft tenants.** If you connect a Microsoft 365 or Azure mailbox over IMAP/SMTP rather than OAuth, authenticated SMTP is disabled by default on tenants created in the last few years, at the tenant level and again per mailbox. The symptom is an authentication failure that looks like a wrong password and is not. Enable SMTP AUTH for the mailbox, or connect over OAuth and avoid it.
- 4**Set the sending name and signature before the first send.** A mailbox that sends its first cold email with no display name and no signature is doing the one thing a brand-new sender should not. Both are per-account settings in Instantly and take a minute across the fleet with bulk edit.
- 5**Set the daily limit deliberately.** The default is not tuned to your mailboxes. This is the single setting that decides whether the fleet lasts, and it is different per platform — see below.

**Connect them yourself or let us do it.** By default we plug the inboxes into your sending tool for you, Instantly included, so the first thing you see is a workspace with the accounts already in it. Say the word on WhatsApp if you would rather have the credentials and do it yourself.

## The daily limit to set on each inbox

One number per inbox per day, and it is not the same on every platform. The [infrastructure calculator](https://warminboxes.com/calculator) sizes fleets on these figures, so setting Instantly to match keeps the tool and the plan agreeing with each other:

| Platform | Cold emails per inbox per day |
| --- | --- |
| Google Workspace | 15 |
| Microsoft 365 | 8 |
| Azure, full tenant of 100 | 2 |
| Azure, 50 per tenant | 4 |
| Azure, 25 per tenant | 6 |

An Azure tenant is billed flat whatever is on it, so a lighter tenant sends more per inbox for the same money.

These are deliberately below what each platform will technically let you push. The ceiling is not the target: the figure that matters is the one an inbox can hold for months without its reputation drifting, and a fleet sending a sustainable number every day beats a fleet that sprints for three weeks and then lands in spam.

**Scale volume by adding inboxes, not by pushing each inbox harder.** Spreading the same sends across more mailboxes and more domains protects every inbox’s reputation and stops one bad domain taking the campaign with it. Put your target volume into the [inbox planner](https://warminboxes.com/inbox-planner) and it works out the fleet.

## Warmup, and why you can leave ours alone

Prewarmed inboxes arrive with weeks of sender history already built, so there is no 21-day wait before the first campaign. Fresh inboxes are warmed by us for 14 to 21 days before handover. In both cases warmup does not stop at delivery: it keeps running at 30 emails per inbox per day underneath your campaigns, for as long as you have the inboxes.

That changes what Instantly’s own warmup is for. Running it as well is not free — every warmup email is a real send from the same mailbox, competing with your campaign for the same daily budget and the same reputation. If you turn it on anyway, count it inside the inbox limit rather than on top of it, or you are quietly sending half again as much as you planned.

**Prewarmed means no warmup wait, not same-day delivery.** The warmup already happened before you ordered, so you can start sending as soon as the inboxes land — which is within 48 to 72 hours, like every other order.

## Sizing the fleet for a target volume

Work backwards from the sends you need, not forwards from the inboxes you fancy buying. At the paces above, a round 1,000 cold emails a day comes out like this:

| Platform | Inboxes for 1,000 a day | Domains |
| --- | --- | --- |
| Google Workspace | 67 | 23 (3 inboxes per domain) |
| Microsoft 365 | 125 | 2 (up to 100 per domain) |
| Azure, full tenants of 100 | 500 | 5 tenants |
| Azure, 25 per tenant | 167 | 7 tenants |

Rounded up to whole inboxes and whole domains. The calculator does the exact arithmetic, including the domain cost.

The shape of that table is the whole argument for choosing a platform on volume rather than on preference. Google is the fewest inboxes for a given volume. Microsoft is cheaper per inbox and needs more of them. Azure is cheapest per inbox at scale and is billed per tenant, flat, whatever is on it — so the lever is how densely you load each tenant, not how many inboxes you buy.

Two tools do this properly: [the calculator](https://warminboxes.com/calculator) if you are sizing by volume, and [the ESP calculator](https://warminboxes.com/esp-calculator) if you know the mailbox providers your list actually sits on and want the fleet sized against them.

## Keeping agency clients apart

If you run campaigns for more than one client out of one Instantly workspace, the thing that hurts later is not the campaigns — it is not being able to tell whose inboxes are whose when something goes wrong at two in the morning. Tag accounts by client when you connect them, not afterwards. Instantly’s per-account tags survive bulk edits and are what you will filter the Unibox on.

Keep domains unshared between clients too. One client’s list quality should not be able to damage another client’s sending domain, and the moment two clients send from the same domain it can. Separate domains are the cheapest insurance on this list: $20 list, currently $12 each if you buy through us, and nothing at all if you bring your own.

## When an inbox starts slipping

Reply rate falling on one account while the rest hold steady, bounces climbing on a single domain, a sudden drop in opens from one provider — these are inbox-level problems, and they are the normal cost of sending cold at volume rather than a sign something is broken.

- 1**Pause that account in Instantly.** The campaign reroutes across the rest of the fleet, which is the reason the fleet exists.
- 2**Check whether it is the inbox or the domain.** Run the domain through the [blacklist checker](https://warminboxes.com/blacklist-checker) and the [grader](https://warminboxes.com/deliverability-checker). A single bad inbox and a listed domain need different responses, and the tools take under a minute.
- 3**Message support.** [+1 904 736 2539](https://api.whatsapp.com/send/?phone=19047362539&text=Hey%2C%20I%20need%20WarmInboxes&type=phone_number&app_absent=0) on WhatsApp, 24/7. Replacement inboxes are part of the package when deliverability drops.
- 4**Keep a few on standby.** A fleet running at its exact ceiling has nowhere to go when one inbox drops out. A few spare accounts mean a flagged inbox is an afternoon’s inconvenience rather than a paused campaign.

## Checks worth running before you load the first list

All free, all ours, none of them needing an account. Five minutes here saves a week of wondering why a campaign underperformed:

- [Deliverability grader](https://warminboxes.com/deliverability-checker) — SPF, DKIM, DMARC, MX, eight blacklists and domain age, graded in one pass.
- [DKIM checker](https://warminboxes.com/dkim-checker) — confirms a key is actually published and tells you when a selector is delegated to a provider that has not published one, which is the most common silent DKIM failure.
- [SPF checker](https://warminboxes.com/spf-checker) — including the recursive lookup count that breaks SPF past ten without any visible error.
- [Blacklist checker](https://warminboxes.com/blacklist-checker) and [SURBL checker](https://warminboxes.com/surbl-checker) — the domain-level lists that affect cold email most.
- [Inbox previewer](https://warminboxes.com/inbox-previewer) — what the email actually looks like in the client before you send it to ten thousand people.

## What the inboxes cost

Prewarmed inboxes include a free prewarmed .COM or .CO domain and send from the day they land. Google and Microsoft are priced per inbox; Azure is priced per tenant, flat, whatever is on it.

| Prewarmed | Billed by | Monthly | 2-monthly | Quarterly |
| --- | --- | --- | --- | --- |
| Google inboxes | inbox | $8.00 | $7.00 | $6.00 |
| Microsoft inboxes | inbox | $8.00 | $7.00 | $6.00 |
| Azure tenants | tenant | $69 | $60 | $50 |

A tenant holds 100 inboxes on one free prewarmed domain, so at full capacity those prices work out at $0.69, $0.60 and $0.50 per inbox.

Fresh inboxes are built on your own branded domains and warmed for 14 to 21 days first, which is why they cost about a third as much at volume: Google from $3.50 down to $2.00 per inbox per month depending on size and cycle, Microsoft 365 from $3.00 to $2.00, and an Azure tenant at $50 flat. Domains bought through us list at $20 and are currently $12; bring your own and there is no domain charge.

Full detail on [the offer page](https://warminboxes.com/offer), and [how it works](https://warminboxes.com/how-it-works) covers what happens between paying and your first send.

## Questions people ask first

Do I need to warm these inboxes before I send?Not on prewarmed inboxes. The sender history was built before you ordered, so you can start cold sending as soon as they land. Fresh inboxes are warmed by us for 14 to 21 days first. Either way our warmup keeps running at 30 emails per inbox per day underneath your campaigns, so you never switch it off.

How many Instantly accounts do I need for 1,000 emails a day?On Google Workspace at 15 a day that is about 67 inboxes. On Microsoft 365 at 8 a day it is about 125. On a full Azure tenant at 2 per inbox it is 500, which is why high-volume Outlook sending is usually run on lighter tenants or on Google. The calculator at warminboxes.com/calculator sizes it exactly, including domains.

Can you connect the inboxes to Instantly for me?Yes. By default we connect the inboxes to your sending tool for you, Instantly included. If you would rather do it yourself you get full admin access to every mailbox and the credentials to plug in.

Should I leave Instantly warmup on as well?It is not needed and it is not free: every warmup email is a send, and warmup traffic competes with campaign traffic for the same daily budget on the same mailbox. Our warmup already runs continuously. If you do turn Instantly warmup on, count it against the inbox limit rather than on top of it.

What happens if an inbox gets flagged partway through a campaign?Pause that account in Instantly so the campaign reroutes to the rest of the fleet, then message support on WhatsApp. Replacement inboxes are part of the package when deliverability drops, which is the reason to keep a few spare rather than running the whole fleet at its ceiling.

Do the domains come with SPF, DKIM and DMARC already set?Yes. SPF, DKIM, DMARC and forwarding are configured before handover, on prewarmed and fresh alike. You can confirm any of it yourself with the free checkers at warminboxes.com/deliverability-tools before you load a single lead.

## Inboxes that are ready for Instantly

Official Google Workspace, Microsoft 365 and Azure mailboxes with SPF, DKIM and DMARC configured before you log in. Delivered in 48 to 72 hours, connected to your sending tool for you if you want.

[Create a free account](https://app.warminboxes.com)[Work out what you need](https://warminboxes.com/calculator)