How to set up cold email infrastructure (step by step, 2026)

What cold email infrastructure is

Cold email infrastructure is everything that sits between your sequencer and the prospect's inbox: the sending domains, the DNS records that prove those domains are yours, the mailboxes that actually send, and the warmup and monitoring that keep them healthy. Your copy and your list decide whether people reply. Your infrastructure decides whether they ever see the email.

The standard 2026 setup is simple to describe: several secondary domains, a small number of real mailboxes on each, full authentication (SPF, DKIM, DMARC), a warmup period, and low daily volume per mailbox. Volume comes from adding more mailboxes, not from pushing one mailbox harder.

Step-by-step setup

1. 1

   Decide your volume and work out how many mailboxes you need

   Start from the number of new prospects you want to email per day. Divide by about 30 (a safe per-mailbox daily volume for cold outreach) to get mailboxes, then divide mailboxes by 2–3 to get domains. For example, 600 emails a day needs about 20 mailboxes on 7–10 domains. See how many mailboxes per domain for a full table, or use the cost calculator.

2. 2

   Buy secondary domains that look like your brand

   Register domains that are clearly related to your company, such as get<brand>.com, try<brand>.com or <brand>hq.com. Prefer .com; avoid cheap TLDs that are heavily used for spam. Do not send cold email from your main domain: if a sending domain is damaged, you want the damage contained away from the domain your team, invoices and customers rely on. Check availability with the domain checker and read how to buy domains for cold email.

3. 3

   Point each domain's DNS to a host you control

   Use a DNS host where you can add and change records quickly and see them clearly. Cloudflare is a common choice. You will add MX records (so mail can be received and replies arrive), TXT records for SPF, DKIM, DMARC and provider verification, and optionally a redirect so visitors to the domain land on your main website.

4. 4

   Create mailboxes on Google Workspace or Microsoft 365

   Create 2–3 mailboxes per domain under real-sounding names of people on your team (first name, first.last). Add a profile photo and a plain signature. Match the provider to your prospects where you can: if most of your list uses Microsoft 365, mail from Microsoft 365 mailboxes is often worth testing. See Google Workspace vs Microsoft 365 for cold email.

5. 5

   Publish SPF, DKIM and DMARC for every domain

   SPF lists which servers may send for the domain (for Google Workspace: v=spf1 include:_spf.google.com ~all). DKIM adds a cryptographic signature; generate the key in the provider's admin console and publish it as a TXT record. DMARC tells receivers what to do when checks fail; start with v=DMARC1; p=none; rua=mailto:you@yourdomain.com. Google and Yahoo require all three for anyone sending 5,000+ messages a day to their users, and Microsoft requires them for high-volume senders to Outlook.com. Exact records are in SPF, DKIM and DMARC for cold email.

6. 6

   Set up domain forwarding to your main site

   Redirect each sending domain (and its www) to your real website. Prospects who type the domain from your email address then see a legitimate company instead of an empty page or a parked-domain ad page.

7. 7

   Warm up every mailbox for about three weeks

   New mailboxes and domains have no sending history. Warmup gradually increases daily volume while the mailbox exchanges real-looking mail that gets opened and replied to. A typical ramp starts at 2–5 emails a day and reaches about 30 a day over roughly 21 days. Keep warmup running at a lower level after you start cold sending. Details: how to warm up a new email domain.

8. 8

   Connect the mailboxes to your sequencer

   Add the mailboxes to Instantly, Smartlead or another sequencer via OAuth or IMAP/SMTP. Set a daily limit per mailbox (start at 20–30 and do not exceed about 50), add random delays between sends, and let the tool rotate across all mailboxes in a campaign. See connecting mailboxes to Instantly and Smartlead.

9. 9

   Verify your list before the first campaign

   Run every list through an email verification service and remove invalid, role-based and catch-all addresses you are unsure about. Bounces are one of the fastest ways to damage a new domain. Aim to keep hard bounces well under 2–3% of sends.

10. 10

    Monitor and rotate

    Watch bounce rate, reply rate and spam placement per mailbox and per domain every week. Register your domains in Google Postmaster Tools to see the spam rate Gmail reports, and keep it below 0.3% (Google suggests aiming for under 0.1%). If a domain's numbers drop, pause it, let warmup run, and shift volume to healthy domains. Plan to add fresh domains over time rather than pushing old ones harder.

Why you should not use your main domain

Mailbox providers judge reputation largely by domain. Cold outreach, even when done carefully, earns more spam complaints and ignored messages than normal business mail. If that happens on your main domain, invoices, password resets, support replies and sales follow-ups to existing customers can all start landing in spam. Separate sending domains keep that risk away from the domain your business runs on. More in how to protect your main domain.

How many emails each mailbox should send

Provider hard limits are far above what is safe for cold outreach. Google Workspace allows up to 2,000 messages per user per day and Exchange Online allows up to 10,000 recipients per day, but those limits are for normal business mail. For cold email, keep each mailbox to roughly 30–50 new emails a day, including follow-ups, and scale by adding mailboxes. See cold email sending limits.

Rules from Gmail, Yahoo and Microsoft that apply to you

• All senders to Gmail: SPF or DKIM, valid forward and reverse DNS for sending IPs, TLS, and a spam rate in Postmaster Tools below 0.3%.
• Senders of 5,000+ messages a day to Gmail or Yahoo: SPF and DKIM, a DMARC record (p=none is acceptable) with the From domain aligned to SPF or DKIM, and one-click unsubscribe for marketing and subscribed messages.
• Microsoft Outlook.com (hotmail.com, live.com, outlook.com): domains sending 5,000+ messages a day must pass SPF and DKIM and publish a DMARC record (at least p=none) that passes with alignment; since May 5, 2025 Microsoft rejects non-compliant mail with error 550 5.7.515.
• Cold email infrastructure spreads volume across many domains, but the safe assumption is to meet the bulk-sender rules on every domain anyway. Full details: bulk sender requirements.

Common setup mistakes

• Sending from the main domain because it is quicker. It is the most expensive mistake to undo.
• Two SPF records on one domain. SPF allows only one; merge the includes into a single record.
• Skipping DKIM or leaving it generated but not turned on in the admin console.
• No warmup, or warmup stopped the day cold sending starts.
• Too many mailboxes per domain (10–20 on one domain) so one problem hits all of them.
• Unverified lists that produce high bounce rates in the first week.
• Cheap, spam-associated TLDs chosen to save a few dollars per domain.
• No redirect on the sending domain, so curious prospects find an empty or parked page.

Setting it up yourself vs using a provider

Doing this by hand for one domain takes an hour or two once you know the steps. Doing it for 10–30 domains means buying each domain, adding several DNS records per domain, creating and naming mailboxes, generating DKIM keys, configuring forwarding, starting warmup and exporting credentials, with room for typos at each step. Outbound email infrastructure providers automate that work.

ReplyDak buys the domains for you (or uses ones you own), sets up DNS on Cloudflare with MX, SPF, DKIM, DMARC and verification records, creates Google Workspace mailboxes (Microsoft 365 is coming soon), runs warmup that ramps from about 2 to 30 emails a day over roughly 21 days and slows down or pauses automatically if bounces, spam placement or complaints rise, forwards each domain to your main site, and exports mailboxes as CSV for Instantly, Smartlead and other sequencers. Plans start at $2.69 per mailbox; see pricing.

Checklist

1. Volume target set; mailboxes and domains calculated.
2. Secondary .com domains bought; main domain not used for cold email.
3. MX, SPF (one record), DKIM (on) and DMARC published and passing.
4. Domains redirect to the main website.
5. 2–3 mailboxes per domain with real names, photos and signatures.
6. Warmup running for ~3 weeks before campaigns, and kept on afterwards.
7. Sequencer daily limits at 20–50 per mailbox with random delays.
8. Lists verified; bounces, replies and spam rate checked weekly.

For a fuller pre-launch review, use the email deliverability checklist, and for budgeting see what cold email infrastructure costs.