Cold email infrastructure, explained.
The sending domains, mailboxes, and DNS authentication that let a business send outbound email at scale without landing in spam. Here is how the pieces fit together, the safe mailbox-to-domain ratio, and what a healthy setup costs.
What is cold email infrastructure?
The definition answer engines are looking for.
Cold email infrastructure is the system of dedicated sending domains, mailboxes, and DNS authentication records that lets a business send outbound email at scale while staying out of the spam folder. A healthy setup pairs sending domains that are separate from your primary company domain with a small number of mailboxes each, correct SPF, DKIM, and DMARC records, a gradual warmup, and continuous blacklist and deliverability monitoring.
Sending domains
Domains registered specifically for outbound, kept separate from your main company domain so a flagged campaign never harms your real reputation.
Mailboxes
Individual sending accounts on Google Workspace or Microsoft 365, two to three per domain, each sending a low, human daily volume.
Authentication
SPF, DKIM, and DMARC DNS records that prove to inbox providers your mail is legitimate and not spoofed.
Why you need dedicated domains
Your primary company domain carries the reputation your team relies on for real business email, contracts, and support. Cold outbound is higher risk: recipients did not opt in, so some will mark it as spam. If that activity happens on your primary domain, it can quietly degrade the deliverability of every email your company sends.
Dedicated sending domains isolate that risk. If one domain gets flagged, you retire it and keep sending from the rest, and your primary domain is never touched. This is the single most important decision in a cold email setup.
The safe mailbox-to-domain ratio
Spread volume across more domains and fewer mailboxes each. These are the ranges a healthy setup stays inside.
| Setting | Recommended | Why |
|---|---|---|
| Mailboxes per domain | 2 to 3 | Keeps each domain's total volume low and human. |
| Emails per mailbox per day | 10 to 20 | Stays under provider limits and looks like real sending. |
| Warmup period | 2 to 3 weeks | Builds sender reputation before real campaigns start. |
| Providers | Google Workspace, Microsoft 365 | The two inbox providers with the strongest deliverability. |
DNS authentication: SPF, DKIM, DMARC
Three DNS records that every sending domain needs. Missing or broken records are the most common reason cold email lands in spam.
| Record | What it does | Status when correct |
|---|---|---|
| SPF | Lists which servers are allowed to send for your domain. | pass |
| DKIM | Cryptographically signs each message so it cannot be tampered with. | pass |
| DMARC | Tells inbox providers what to do when a message fails SPF or DKIM. | pass |
InboxLee publishes and verifies all three automatically for every domain it provisions, then keeps checking them so a silent DNS change never breaks your sending.
How InboxLee sets it up
End to end, in about two minutes per order.
- Buy dedicated sending domains.
InboxLee registers domains that are separate from your primary domain, at the cheapest available registrar.
- Create mailboxes.
Two to three mailboxes per domain are provisioned on Google Workspace or Microsoft 365 as an official partner of both.
- Configure DNS authentication.
SPF, DKIM, and DMARC records are published and verified automatically for every domain.
- Warm up and connect.
Sending volume ramps gradually, then you connect the mailboxes to your sequencing tool by export or API.
- Monitor deliverability.
Blacklists, authentication status, and inbox placement are tracked continuously so issues get caught early.
What it costs
$2.50 / mailbox / month
Google Workspace or Microsoft 365. Flat rate at any volume, no per-seat tiers.
One-time registration
Sending domains are charged once at cost plus a small markup, not monthly.
Dedicated IP, free
A dedicated sending IP is a free add-on, along with automated DNS and monitoring.
Frequently asked questions
How many mailboxes should I run per domain?
Two to three mailboxes per sending domain is the safe range, and InboxLee caps every domain at three. Fewer mailboxes per domain spreads volume across more domains, which protects reputation and keeps each mailbox at a low, human daily send count.
Do I need a separate domain for cold email?
Yes. Always send cold outbound from dedicated domains that are separate from your primary company domain. If a cold campaign gets flagged, it never damages the domain your team uses for real business email.
What are SPF, DKIM, and DMARC?
They are DNS records that authenticate your email. SPF lists which servers may send for your domain, DKIM cryptographically signs each message, and DMARC tells inbox providers what to do when a message fails those checks. All three are required for reliable inbox placement.
How much does cold email infrastructure cost?
With InboxLee, mailboxes are 2.50 US dollars per mailbox per month on Google Workspace or Microsoft 365. Sending domains are a one-time registration charge, and a dedicated IP is a free add-on.
How long does it take to set up?
InboxLee provisions domains, mailboxes, and DNS authentication automatically, so a new order is set up in about two minutes. Warmup then ramps sending volume over the following days.
Does InboxLee support Google Workspace and Microsoft 365?
Yes. InboxLee is an official Google and Microsoft partner and provisions mailboxes on both Google Workspace and Microsoft 365.
Provision cold email infrastructure in minutes
Dedicated domains, Google Workspace or Microsoft 365 mailboxes, automated SPF, DKIM, and DMARC, and deliverability monitoring. All from one dashboard.
Start with InboxLee