Never send cold email from your main domain
Your main domain carries your client emails, invoices and proposals, so it never sends cold email. Cold email goes out from secondary domains instead: proxy domains that look like yours, redirect to your main site, and each hold a few inboxes.
The reason is spam complaints. Google’s spam complaint limit is 0.3%, and it recommends staying under 0.1%. If a secondary domain gets flagged, your client emails still land.
How many inboxes per domain: Google vs Azure
Two numbers decide the whole setup: how many emails one inbox sends a day, and how many inboxes fit on one domain.
| Measure | Azure | |
|---|---|---|
| Inboxes per domain | 3 | Up to 75 |
| Emails per inbox a day | 15 | 4 |
| Emails per domain a day | 45 | 300 |
To size your own setup, divide your daily volume by the emails per inbox to get the inboxes, then divide the inboxes by the inboxes per domain to get the domains. Round up both times.
What happens when a domain burns
When a domain burns, you keep the inboxes you paid for and only swap the domain, at $12 each. Replacing 300 emails a day of volume means 7 new domains on Google ($84), or 1 on Azure ($12).
The trade-off is that on Azure, all that volume sits on one domain. With 75 inboxes on one domain, spam complaints pile up faster, so in theory an Azure domain can burn sooner. Each Azure inbox sends only 4 emails a day, though, so the volume is spread across far more inboxes.
What it costs at 2,000 emails a day
| Setup | Inboxes | Domains | Per month |
|---|---|---|---|
| All Google | 134 | 45 | $469 |
| Half and half | 317 | 27 | $433.50 |
| All Azure | 500 | 7 | $281.50 |
Google inboxes are $3.50 a month each. The Azure plan is $199 a month for 350 inboxes, plus $0.55 for each one after that. Domains are $12 a year, paid in the first month. Over the first year, domains included, all Azure costs about 44% less than all Google. These are example prices from November 2026.
Run your own volume in the Inbox Calculator, where every result shows its math.
Check your domains on Spamhaus every week
Spamhaus keeps a free blocklist of domains flagged for spam. Check every domain every week, starting with your main one. A listed domain is burnt: stop sending from it and replace it.
Build in November and December, send in January
Warming new inboxes takes 3 to 4 weeks. With the holiday season close, build your domains and inboxes in November and December, so they’re ready when you start sending in January.
The providers we use
If you’d rather set it up yourself, these are the providers we use for our clients. For Azure inboxes, Sending.ac. For Google inboxes, Zapmail and Premium Inboxes.
The providers we use for our clients
Some of these are affiliate links: we may earn a commission at no cost to you. We only list tools we use for client campaigns.
Questions
How many inboxes per domain should I use for cold email?
On Google Workspace, 3 inboxes per domain at 15 emails a day each, so 45 emails a day per domain. On Azure, up to 75 inboxes per domain at 4 emails a day each, so 300 emails a day per domain.
Are Azure inboxes cheaper than Google inboxes for cold email?
At volume, yes. At 2,000 emails a day, all Azure costs $281.50 a month and all Google costs $469, using November 2026 example prices. Over the first year, domains included, Azure is about 44% cheaper.
What's the downside of Azure inboxes?
Much more volume sits on each domain: up to 75 inboxes instead of 3. Spam complaints add up per domain, so in theory an Azure domain can burn sooner. Each Azure inbox sends only 4 emails a day, which spreads the volume across far more inboxes.
How long does it take to warm up new cold email inboxes?
Warming takes 3 to 4 weeks, so build your domains and inboxes about a month before you want to start sending.
Read the video transcript
Did you know that you could be paying 44% less for the exact same cold email volume? The math is simple, but the decision is not. But first, what are we talking about again? Well, sending cold emails to your ICP or ideal customer profile, just not from your main domain. Now this is my company's main domain. I use it to communicate with clients, send invoices and proposals, send team emails and so on and so forth, but I would never send cold emails from my main domain. And the reason is super simple. Google enforces a strict maximum spam complaint threshold of 0.3%. If you do the math, it's three complaints per 1000 emails delivered.
However, Google recommends you to keep this below 0.1%. So if you think about it, if you use your main domain to send cold emails, there is a possibility for Google to mark you as a spam or bulk sender if your spam complaint threshold exceeds 0.3%. Now the fix is super simple. All you got to do is set up proxy or burner domains that would redirect to your main domain and then you would set up inboxes under these proxy domains. So whenever you send an email and somebody wants to check the website, they absolutely can and would automatically redirect your main domain.
Here's a quick tip, set up a cron job on a weekly basis to check your domains on spamhaus.org and if they're listed, replace them with new ones. Here's what a non-listed domain looks like on spamhaus.org. This eventually is going to get listed because I'm using it for cold emails. And here's what a listed one looks like. Now let's talk about the kinds of inboxes that you can set up. If an organization has one domain and a thousand employees, all the inboxes would be set up under that one domain. But in the context of cold email, do not get marked as a bulk sender. Using Google, it is recommended to only send 45 emails a day at max from one domain. The breakdown is 3 inboxes at 15 emails per day per inbox. Now with Azure, you can set up a maximum of 75 inboxes per domain. Each inbox can send four emails per day, totaling 300 emails per day per domain which is exactly why Azure is cheaper. Now, if you compare Google and Azure inboxes like anything else, there are trade-offs. Let's talk about the first one real quick. So whenever a domain burns, by that I mean if it gets listed on spamhaus.org, your next step would be to replace that specific domain. Now let's say hypothetically in both cases a sending volume of 300 a day has been affected.
If that happens with your Google infrastructure, you're looking at a replacement cost of $84 because you got to replace seven domains that are basically responsible for 300 per day of sending volume, but that Azure, you just got to replace one domain equivalent to $12 in cost. This one is in favor of Azure. The second one is a little technical. If you go back to Google spam complaint threshold, which is ideally in maximum of 0.3%, keeping that in mind, one domain for Azure is responsible for 75 inboxes as opposed to one domain for Google responsible for three inboxes. So looking at it from this lens, if we were to talk about 300 emails per day with Azure, it's all on one domain. And then with Google they're on seven different domains. So your sending is diversified. So there is a higher likelihood for Azure inboxes to get burned fast from this lens. But on the other hand, each Azure inbox is only sending four emails, but each Google inbox is sending 15 emails. As I said the second trade-off is a little confusing. Now for the exciting part, how much is it going to cost for me to send anywhere from 1,000 to 5,000 emails per day? For a sending volume of 1,000 emails per day, you're looking at an ongoing cost of $234.50. However, your first month's setup fee is going to be $510.50 because your inboxes are diversified across a lot of different domains. Moving on to Azure. You can send a minimum of 1400 emails per day, but even at 1400, which is 400 emails per day extra, as opposed to Google, you're still looking at a lower cost. And the setup fee is also significantly low. At a thousand emails a day, you have a price difference of roughly 22 to 25%. But from 2000 emails and upwards, you're looking at a price difference, which is huge of 44% per month. Let's quickly talk about the 2000 per day sending volume. So all Google is going to cost you $470 per month. A lot of people to diversify their portfolio, they set up half and half. So half Azure and half Google. That's basically going to cost you $433.50 per month. And the first month is going to cost $760. All Azure as compared to all Google is 44% less in terms of pricing. The first month including domains would cost $365.50. On an ongoing basis, it would cost $281.50. Here's the math for all three of them. You can pause the video and look at it.
Now, if you want to set up your email infrastructure yourself, you can go for the following providers. Quick disclaimer, this is not sponsored. For Google inboxes, I would recommend either a Zapmail or Premium Inboxes. We use both for our clients. And for Azure, I would recommend Sending.ac. We definitely use them for our clients. If you made it this far, there's a higher chance that you're interested in cold email. That's the case holiday season is approaching so I recommend you to set up your email infrastructure because warming up of email infrastructure takes at least three to four weeks of time. So you can use November and December to think about list building, copywriting, email infrastructure and so on and so forth. Warm up your email infrastructure for three to four weeks and then January you start sending.
That's pretty much it for this video. If you have any questions related to email infrastructure or cold email, link for the same is in comments.
Lightly edited for clarity.