Mailboxes are the cheapest growth lever in B2B: what cold email infrastructure costs
Mailboxes are the cheapest growth lever in B2B, and most people buy them at ten times the price.
Three calls in July put real numbers on it. On July 3 we priced mailboxes bought inside a popular sending tool. On July 16 we set a target cost per mailbox for our own stack. On July 20 Amir demoed the automation that takes a fresh domain all the way to a live campaign, and we priced the sending layer underneath it. Here's what it costs when you stop paying retail.
The 10x markup
On July 3 we looked at buying mailboxes inside Instantly: about $10 per mailbox per month. A hundred mailboxes comes to around $1,000 a month. Our own setup did the same job for roughly a tenth of that.
That gap came up again on our July 13 team call, in plainer words: clients "would pay 10x on instantly for the same setup." Same mailboxes, same sending, same warmup. The difference is who assembled it.
I'm not knocking the convenience. Buying inside the tool is fast and it works. But if you're running at volume, convenience is a line item that grows with every mailbox you add, and mailboxes are the one thing you'll keep adding.
Our own stack: domains, host, sender, warmup
A cold email system has four cost layers, and only one of them is expensive if you buy smart.
- Domains. A handful of secondary domains so your main domain never sends. Cheap, bought once a year.
- Hosting for the mailboxes. On July 20 we were on a DirectAdmin host at about $29 a month with unlimited domains and mailboxes. The line on the call: "$29 a month sorry but then you get unlimited everything."
- The sending layer. The service that pushes the mail out. This is where volume pricing matters.
- Warmup and the sequencing tool on top. A fixed cost, not per mailbox if you set it up right.
On July 16 we set the target for the whole thing at about $1 per mailbox per month, against the $5 to $10 you'll see in common tools. Amir's automation is what makes that number possible, because the expensive part of cheap infrastructure is the human time to set it up. Once a domain goes to a working campaign without someone clicking through 40 screens, the hosting bill is the only bill.
SES versus SendGrid on cost
On July 20 we also priced the sending layer. Amazon SES runs about $0.10 per 1,000 outbound emails with no monthly fee, which is about $100 per million emails. Our notes from the call put the equivalent volume on SendGrid at around $600.
Six times cheaper on the sending layer is real money at scale. It's not the whole story, though. The cheapest sender isn't worth it if you can't manage its reputation, and every provider has its own rules on what it'll carry. Price the sender last, after you know you can run it cleanly.
What the cheap part buys you: volume
Here's why this matters beyond saving money. Infrastructure is the one place in outbound where spending less lets you do more.
Each mailbox should send a small number of emails a day to stay healthy. So your daily volume is your mailbox count times a small number. If mailboxes cost $10 each, adding 100 is a budget conversation. If they cost about $1, adding 100 is a Tuesday.
In practice it showed up on the calendar. By July 14 Charles was booked three weeks out and I was booked about a week and a half out. That is what cheap volume looks like from the inside: not a nicer dashboard, a fuller calendar.
Where the money should go instead
If infrastructure is the cheap layer, the budget should move to the two layers that decide whether volume turns into meetings.
The list. On July 16 we were pricing contacts at about 1 cent each. Cheap data is fine as long as you verify it, but the targeting decisions on top of that data, who you pick and why, are where the time should go. A cheap mailbox sending to the wrong person is still waste.
Follow-up. Most of the money in outbound is lost after the reply, not before it. Someone has to answer interested replies fast, book them, and keep the calendar moving. That's people time, and it's where we'd rather spend than on mailbox markups.
The hidden cost: setup time and breakage
Cheap infrastructure has one honest catch, and it showed up on our July 13 call. The setup is fiddly. One of our domain registrars had started refusing mailboxes, which was causing delays of about three days before new mailboxes could be plugged in. When you buy inside a sending tool, that's their problem. When you build your own, it's yours.
That's why the automation matters more than the hosting deal. A $29 host with unlimited mailboxes is only cheap if spinning up the next 100 mailboxes takes minutes, not a weekend. Budget for the tooling or the person who builds it once, and the per-mailbox cost stays near a dollar for as long as you run.
A rough way to sanity-check your own setup: divide your monthly infrastructure bill by your mailbox count. If you're well above a couple of dollars a mailbox and you're running more than a few dozen, you're paying for convenience you could build once.
If you want to see what more volume would mean for your pipeline, run your own numbers on the ROI calculator.
Frequently asked questions
How much does cold email infrastructure cost?
It depends on who assembles it. In July, mailboxes bought inside a sending tool ran about $10 each per month, while our own stack targeted about $1 per mailbox using a $29-a-month host with unlimited mailboxes.
Is Amazon SES cheaper than SendGrid?
On price, yes. SES is about $0.10 per 1,000 emails with no monthly fee, about $100 per million, and our notes put the SendGrid equivalent around $600. Reputation management matters more than the per-email price.
How many mailboxes do I need?
Enough that each one sends a small daily volume and the total covers your list. Work backward from the emails per day you need, and keep each mailbox's load low to stay healthy.