The Warmup Settings I Actually Set in Instantly Before a New Domain Sends a Single Cold Email

I build and run cold email infrastructure for B2B clients, 2000+ meetings booked for B2B clients so far through this exact kind of setup. Most warmup advice ends at buy domains, flip warmup on, wait three weeks. The dashboard itself has about eight settings that decide whether any of that actually works, and almost nobody explains what to put in them. So here is a walkthrough of the actual numbers, straight from how I set up a client's infrastructure on camera.

What warmup settings should you actually use?

Cap warmup at no more than 50 emails per mailbox a day, but actually set the daily warmup limit closer to 10 to 15. Set your daily inbox placement tests to match the real volume you plan to send once live, not a generic number. Put reply rate around 30%, open rate around 60%, spam protection around 90%, and mark important around 45%. Increase the ramp by one or two emails a day, and give it about two weeks before launch. Keep it running after that, just at a lower share of the mailbox's volume.

None of those numbers are magic. They are the settings I'd point a client to on day one, because guessing at them is how a new domain ends up in spam before it ever reaches a real prospect.

Why the dashboard matters more than flipping a switch

A cold email setup only works if it is cost effective, spread across more than one provider, reliable without you babysitting it, able to add volume when you need it, and set up correctly on the authentication side, SPF, DKIM and an unsubscribe option included. Most of that is decided before you ever open a warmup tool, by which domains and mailboxes you bought and how you split them. The warmup tool is where a correctly built setup either earns the reputation it needs, or quietly fails because the defaults were left alone.

Email providers got stricter with their rules this year, strict enough that a number of outbound agencies closed because they could not keep up. That is the bar a solo founder or a small in-house team is also being held to now, whether they know it or not.

Split domains across three kinds of providers

Buy sending domains through a platform built for it rather than a generic registrar. In the walkthrough I use Primeforge, which lets you buy domains for Google Workspace or Microsoft 365 from one dashboard, suggests close variations of your real domain to register, and forwards the vanity domain back to your main site so the purchase reads as deliberate rather than throwaway. For an agency, it also keeps every client's domains in a separate workspace instead of one shared pool.

The platform split matters because it should roughly match who you are emailing. If your list is mostly Gmail accounts, send from Google domains. If it is mostly Microsoft 365 accounts, send from Microsoft domains. As a starting mix, I go close to a 50/50 split, then lean it toward whichever platform your actual market uses more. For a US only list I'd lean closer to 70% Microsoft and 30% Google, and for a European list closer to 60% Google and 40% Microsoft. On top of Google and Microsoft, I also run a third pool through a custom SMTP provider such as Maildoso, so a policy change at either Google or Microsoft only touches part of the fleet, not all of it.

Why I cap it at two or three mailboxes per domain

Diversifying is not just across providers, it is across domains too. I do not put more than two or three mailboxes on a single domain plan. The more horizontally spread your sending is across separate domains, the less damage one flagged domain does to the whole fleet, and the longer the whole system holds up. When you need more sending volume, the answer is more domains and mailboxes, not more mailboxes crammed onto the domains you already own.

Pricing on Primeforge, as shown in the walkthrough, runs about 12 to 20 dollars a year per domain and 2.50 to 3.50 dollars a month per mailbox, depending on which options you pick. That is cheap enough that there is rarely a good reason to overload a domain to save a few dollars.

The warmup ceiling, and where I actually set mine

Inside Instantly, the first number to set is the daily warmup volume per mailbox, and I would not put this above 50 emails a day under any circumstance. In practice I set it much lower than that ceiling, closer to 10 to 15, with a minimum wait time of one to three minutes between sends so the activity does not look scripted. If a mailbox is brand new, I leave the campaign slow ramp option on. Once it has warmed up properly, I turn that specific setting off, since it was only there to protect a fresh account.

How many inbox placement tests should you run a day?

This is the setting I see skipped most often, and it is a simple one: your daily inbox placement tests should match the volume you actually plan to send once the domain goes live. If your real plan is 15 cold emails per mailbox per day, set 15 placement tests per day per account during warmup too, not a round default number the tool suggests. The test should rehearse the real send pattern, not a different one.

Fifteen a day as the eventual send volume is more conservative than the 20 to 30 emails per mailbox per day I usually run once an account is fully warmed and proven, but it is a reasonable, safe number to warm toward and start from if you are setting a domain up for the first time.

The math that follows from this is simple. Take your planned daily send volume and divide it by the per-mailbox number you land on. Plan to send 300 cold emails a day at 15 per mailbox, and you need 20 mailboxes. Cap each domain at two or three mailboxes, and 20 mailboxes means 10 domains. Swap in your own target volume and the same division gets you your own number.

What the reply rate and spam protection numbers do

A few more sliders decide how human the warmup traffic looks to a spam filter. Reply rate around 30% is enough, since nobody who sends real cold email gets a reply to every message either, and 100% would read as obviously automated. Open rate around 60%, spam protection around 90%, and mark important around 45% round out a profile that looks like normal mailbox activity rather than a bot farm emailing itself. In the advanced settings, I also turn on read emulation, which has the tool simulate actually reading the email content rather than just opening and closing it.

Once these are set and running, the tool scores each mailbox's health. Anything from 95 to 100 is a strong score. If a mailbox sits noticeably below that, the first thing to check is whether the custom tracking domain setting below is actually turned on.

The tracking domain setting most people skip

Every mailbox should get its own custom tracking domain rather than using the warmup tool's shared default. In Instantly this means adding a CNAME record, typically something like int.yourdomain.com, then verifying its status, CNAME, and SSL inside the dashboard. A dedicated tracking domain tied to your own sending domain reads as more deliberate to a spam filter than a generic one shared across thousands of other accounts using the same tool, and it is one of the first things worth checking if a mailbox's health score will not climb.

The ramp: how fast to increase, and when it is ready

Start small, three to five warmup emails a day, and increase by one or two a day from there rather than jumping straight to your target number. Running it this way, a domain is usually ready inside about two weeks. That lines up with the general rule that a new domain needs real time before it carries any cold outreach at all. I go through the full week by week version of that rule, including why the window has stretched in the last year, in how to warm up cold email domains.

Why warmup should never fully switch off

A common habit is treating warmup as a one-time setup step: run it for two weeks, turn it off, start sending. Keep it running in the background even after a domain goes live, just at a smaller share of the mailbox's daily volume than during the initial ramp. A mailbox that stops warming the day it starts cold sending loses the steady signal that kept it looking trustworthy in the first place.

Once a domain has been live for a while, I also rotate mailboxes in and out of active sending on a schedule, which does for an established fleet what warmup does for a new one. I cover that system in the mailbox rotation trick for cold email. And after launch, the DMARC reports your domain's DNS provider sends weekly are the clearest outside signal that authentication is still configured correctly, which is worth checking even when a mailbox's health score inside the warmup tool looks fine. I walk through what those reports actually say in how to read a DMARC aggregate report.

What this setup actually costs a month

For 10 domains and 20 mailboxes, at roughly 15 to 20 dollars a year per domain and 3 dollars a month per mailbox, the domain cost works out to about 12 to 17 dollars a month once spread across twelve months, plus about 60 dollars a month for the mailboxes themselves. That is an assumption built from the pricing shown in the walkthrough, not a quote you should treat as fixed, since pricing changes. On top of that sits whatever your warmup and sending tool charges per account. It adds up to a setup that is cheap relative to the outbound budget it supports, which is also why there is rarely a good excuse to skip steps like a dedicated tracking domain to save a few dollars a month. If you would rather have this built and monitored for you instead of doing it by hand, I go through what that service actually includes in cold email infrastructure services: what you're buying.

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