Cold email infrastructure is the set of domains, mailboxes, and DNS records your campaigns actually send from. It is the foundation everything else sits on, and the order you build it in matters. Set it up wrong and you spend weeks unwinding it.
This is the setup sequence from scratch. Follow it in order. Each step depends on the one before it.
What cold email infrastructure means
When you send a cold email, it leaves from a mailbox, which lives on a domain, which has DNS records that tell the world who is allowed to send for it. That stack is your infrastructure. The sending tool sits on top of it, but it is not the infrastructure itself.
The reason this gets its own guide is that almost every deliverability problem traces back to an infrastructure decision: the wrong domain, no authentication, too few mailboxes pushed too hard. Get the foundation right and the rest of cold email gets dramatically easier.
Step 1: Buy your sending domains
The first rule of cold email infrastructure: never send from your primary domain. If a cold campaign damages reputation, you do not want that anywhere near your main domain or your team's everyday email.
Instead, register separate sending domains. These are usually close variations of your brand name. Each one is a distinct reputation, isolated from your primary domain and from each other. Buy them well before you plan to send, because they need age and warmup before they are useful.
Step 2: Set up mailboxes
On each sending domain, create mailboxes. These are the actual email accounts your campaigns send from, hosted on a provider like Google Workspace or Microsoft 365.
Each mailbox should send a conservative daily volume. The way you scale cold email is by adding mailboxes, not by pushing existing mailboxes harder. More mailboxes at a low per-mailbox rate is far safer than a few mailboxes at a high rate. You can model the math with the free mailbox calculator.
Step 3: Configure DNS and authentication
With domains and mailboxes in place, set up the DNS records that make them trustworthy. This is non-negotiable and it comes before any sending.
- MX records so mail can be received, which matters for replies and for looking like a real domain.
- SPF, a single record listing every service allowed to send for the domain.
- DKIM, a signing key published for each sending platform you use.
- DMARC, a policy record, started in monitoring mode.
The SPF, DKIM and DMARC guide walks through each one, and the free authentication checker confirms they all pass before you move on. Do not skip the verification step. DNS fails silently.
Step 4: Warm up every account
Domains and mailboxes are configured, but they have no reputation yet. Sending real campaigns now would look exactly like a spammer spinning up burner accounts.
Warm up every mailbox with a gradual ramp before it touches a campaign. Plan on two to three weeks. The warmup guide covers the schedule, and a tool with human-like warmup runs the ramp across all your mailboxes at once instead of you doing it by hand.
Step 5: Connect a sending tool
Only now does the sending platform enter the picture. It connects to your warmed mailboxes and runs the campaigns, sequencing, and tracking on top of the infrastructure you built.
This is also where the dedicated versus shared IP question gets decided. Many tools route all of this through a shared IP pool, which means the infrastructure work you just did sits on a reputation you do not fully control. SendKit gives every account dedicated IPs and isolated infrastructure, and can provision mailboxes directly, so the whole stack stays under your control. The dedicated vs shared IP guide covers why that matters.
How many domains and mailboxes do you need
It depends entirely on your target volume, which is exactly why the order in this guide matters. You work backward from how many emails you need to send.
Start from a conservative daily send per mailbox. Divide your target daily volume by that number to get your mailbox count. Then spread those mailboxes across multiple domains so no single domain carries all the risk. The mailbox calculator does this math for you. The instinct to over-provision is usually wrong early on. Build for the volume you will actually send in the next quarter, warm it properly, and add more domains and mailboxes as you scale.
Infrastructure is the least glamorous part of cold email and the part that decides everything else. Build it carefully once, in this order, and you rarely have to think about it again.