How to Set Up Cold Email Infrastructure

To set up cold email infrastructure: buy separate sending domains, add SPF, DKIM and DMARC to each, create up to 5 mailboxes per domain, warm every mailbox up for 14 days, then send up to 25 cold emails per mailbox a day from a sequencer and watch placement per mailbox. For 300 emails a day that is 12 mailboxes on 3 domains.

Cold email infrastructure is the technical setup behind your outreach: the sending domains, the mailboxes, their DNS records and the software that sends and monitors your mail. It decides whether your emails reach the inbox. If the setup is weak, good copy does not help: the messages land in spam.

This post is the setup, in the order you build it. To choose a vendor, read the best cold email infrastructure providers, compared on cost, warmup and sending. Our own setup, with mailboxes, warmup and sending in one $2.50 subscription, is on cold email infrastructure; prices are on pricing.

What Is Cold Email Infrastructure?

The goal is simple: mail from your domains should look trustworthy to receiving providers like Google and Microsoft.

They judge that by your sender reputation: how your domains and IP addresses have behaved in the past. A good reputation gets mail into the inbox; a poor one sends it to spam, however good the content.

Core Components of Your Cold Email Setup

A working setup has four parts. Together they protect your main business domain, keep deliverability high and keep your domains off blocklists.

Skip one and the others cannot make up for it. The order below is the order you build them in.

Deliverability is the result of this setup. Since February 2024, Google asks all senders to keep the spam rate in Postmaster Tools below 0.1% and never reach 0.3%, and requires SPF, DKIM and DMARC from anyone sending 5,000 or more messages a day to Gmail accounts (Google sender guidelines). Microsoft requires SPF, DKIM and DMARC from domains that send 5,000 or more messages a day to Outlook.com, Hotmail.com and Live.com addresses; since May 5, 2025 non-compliant mail is rejected with 550 5.7.515 (Microsoft support).

Building Your Technical Foundation

Build your cold email infrastructure in this order: domains, DNS records, mailboxes, sending software.

A key rule of cold emailing is never use your primary business domain for outreach. Your main domain (yourcompany.com) carries mail to clients, investors and your team. If outreach from it gets marked as spam, all of that mail suffers.

Buy dedicated domains for outreach, such as getyourcompany.com or yourcompany.io. Cold email problems then stay on those domains.

Set Up SPF, DKIM and DMARC

Three DNS records tell Google and Microsoft that mail from your new domains is legitimate. Set up all three on every sending domain:

• SPF (Sender Policy Framework): Specifies which servers can send emails on your behalf, preventing unauthorized messages.

• DKIM (DomainKeys Identified Mail): Adds a digital signature to verify email integrity during transit.

• DMARC (Domain-based Message Authentication, Reporting & Conformance): Checks that SPF or DKIM passed for your From domain, tells receivers what to do with mail that fails, and sends you reports.

Test them after setup; our SPF, DKIM and DMARC test guide shows how.

Choosing Your Email Providers and Sending Software

You need mailboxes and a tool that sends the campaigns. Mailboxes run on Google Workspace, Microsoft 365 or a provider built for cold email; Outreach2day, which we make, sells SMTP/IMAP mailboxes with warmup and a sequencer in one $2.50 subscription, so both jobs sit on one bill. Send campaigns from a dedicated tool that handles scheduling, personalization and mailbox rotation. When choosing bulk email sender software, check that it connects to your mailbox provider and supports your volume.

Warming Up Your Accounts

A new mailbox that suddenly sends hundreds of emails looks like a spammer's account. Before any campaign, build a sending history with warmup, so Google and Microsoft see normal behavior.

Warm Up for 14 Days Before Cold Volume

Send no cold email for the first 14 days, only warmup. From day 14 each mailbox sends the full volume, up to 25 cold emails a day. Keep warmup running after that. On Outreach2day each mailbox sends 25+ warmup emails a day to Google recipients, 25 to Outlook and 25 to other providers.

If placement drops, lower the volume until it recovers. The day-by-day plan and the checks before cold email are in how to warm up a new email domain.

Why Warmup Matters

Skip warmup and your first campaign can land in spam or put the domain on a blocklist. Then the domains, DNS work and mailboxes you paid for are wasted.

Plan 14 days of warmup before the first cold email and about 21 days before full volume.

Warmup can be automated: an email warmup service sends, opens and replies to messages for you, and the best email warmup tools post compares ten of them.

Keeping Your Infrastructure Healthy

Once campaigns run, your cold email infrastructure needs monitoring. Problems start small: one mailbox slips into spam, one list bounces. Track the numbers below every week, and daily at high volume.

Metrics to Track

A sudden change in any of these needs attention the same day. To check the reputation behind them, see how to check your email domain reputation.

• Bounce rate: a rising rate points to an unverified or outdated list. Verify addresses before sending.

• Spam complaint rate: Google asks all senders to keep the spam rate in Postmaster Tools below 0.1% and never reach 0.3%.

• Reply rate: a drop with unchanged copy and list usually means mail has started landing in spam. Open rates are unreliable for this: Apple Mail Privacy Protection downloads remote content, including tracking pixels, in the background when a message arrives (Apple).

Bad numbers hurt the domain's reputation for future campaigns too.

What to Do When Metrics Drop

Do not keep sending and hope it passes. When the numbers turn:

1. Pause Campaigns: Halt all emails from affected domains to avoid worsening the problem.

2. Identify the Issue: Use tools to check for blacklists, like Spamhaus, and analyze campaign data to find the cause—whether it’s a bad list or aggressive content.

3. Clean Your Lists: Remove unverified or dubious email addresses to reduce bounce rates.

4. Revise Your Message: Rewrite misleading subject lines, remove link shorteners and cut aggressive sales language.

Resume at a lower volume and raise it again slowly.

How to Scale Your Outreach Safely

Scaling your cold email infrastructure means adding capacity: more mailboxes and domains. Raising volume too fast burns the domains you just warmed up.

Spread Sending Across Domains

A single domain or a handful of mailboxes is a single point of failure. Spread sending across several domains and many mailboxes:

• Domain Rotation: Distribute your sending volume across all domains.

• Mailbox Rotation: Automatically switch between sender mailboxes for each campaign.

• Gradual Ramping: Add new, warmed-up mailboxes instead of raising the daily limit of existing ones past a safe level.

If you repeat this setup for many clients, a cold email API lets your scripts buy domains, run warmup and add mailboxes to your sequencer.

Keep Personalization at Scale

Volume tends to lower quality, and prospects recognize a template. A {{firstName}} tag is not personalization. Segment the list by industry or role and write the opening line for the segment, or reference something specific to the company, such as recent news.

Using AI Without Sounding Like AI

AI makes it easy to write personalized lines at scale, and many recipients say they can tell. In a July 2024 survey of 1,869 US adults by EmailToolTester, 61.4% said they think they can spot an AI-generated cold email, and 44.4% said they would be less likely to engage with one that was clearly AI-written (EmailToolTester). Use AI for research and drafts; edit every template so it reads like a person wrote it.

Cold Email Infrastructure FAQ

Common questions when setting up cold email infrastructure for the first time.

How Many Domains and Mailboxes Do I Really Need?

Work backwards from your daily volume. We recommend up to 5 mailboxes per domain and up to 25 cold emails per mailbox a day, excluding warmup. For 300 emails a day, that means 12 mailboxes on 3 domains. These are starting points, not provider limits; adjust them to your placement results. See mailboxes per domain.

Should I Use My Main Company Domain?

No. Do not use your primary business domain (e.g., yourcompany.com) for cold outreach. If it gets flagged, your everyday company mail is filtered too.

Use separate domains for outreach. Variations like getyourcompany.com or yourcompany.co work well.

Which Email Provider Is Best?

Our pick is Outreach2day (we make it): SMTP/IMAP mailboxes on your own domains at $2.50 a month each, with warmup, a sequencer, per-mailbox analytics and Google and Outlook placement tests included. Google Workspace and Microsoft 365 are the other common choice, with a sequencer bought separately. The full ranking, with the cost of each setup at 25, 100 and 400 mailboxes, is in best cold email infrastructure providers. Whatever you choose, test placement per provider: mail from the same mailbox can land in the inbox at Outlook and in spam at Gmail.

Why Do My Emails Still Go to Spam Sometimes?

Some mail will land in spam even with a correct setup: corporate filters and security gateways apply their own rules. Zero spam placement is not a realistic target. Aim for most of your mail in the inbox, and investigate when placement drops for one provider or one domain.

Outreach2day sets up cold email infrastructure for you: domain registration, mailbox creation, SPF, DKIM and DMARC, automatic warmup and health monitoring.