Cold email infrastructure setup in 2026

Domains vs mailboxes vs IPs

People new to outbound often treat “an email account” as one thing. To a receiving mail server it is at least three, and they are judged separately.

Domains: the name your reputation is attached to

Gmail, Outlook and Yahoo increasingly score mail by the domain in the From address and the domains that sign it. That is why the first rule of cold email is to never send it from your main company domain: if a campaign goes badly, you do not want the domain that carries your invoices, password resets and customer support to inherit the damage. Instead, register a handful of secondary domains that are obviously yours (getacme.com, acmehq.com, tryacme.io), point their websites at your main site, and send outbound from those.

Every sending domain needs its own SPF, DKIM and DMARC records, an MX record so replies and bounces have somewhere to go, and ideally MTA-STS and TLS-RPT. Domains are cheap; losing your primary domain’s reputation is not.

Mailboxes: the identities that send

A mailbox is a real address with a real person’s name on it, like lena@getacme.com. Mailboxes are how you split volume: instead of one address sending 1,000 messages a day, which looks like a bulk sender and is treated as one, thirty-odd addresses each send a volume that looks like a busy salesperson. The usual practice is two or three mailboxes per domain, so that one domain’s trouble only affects a few senders.

IPs: where the mail physically leaves from

Every message is delivered from an IP address, and receivers track the reputation of that address too. With Google Workspace or Microsoft 365, your mail leaves from the provider’s large shared ranges, which you neither control nor see. With a dedicated IP, the address is yours alone: no other sender’s spam complaints can drag you down, but you also start with no history and have to build it. The IP also needs a valid PTR (reverse DNS) record that matches its forward DNS, which both Google and Yahoo now require of every sender.

How the numbers fit together

Work backwards from the number of new prospects you want to reach per day. Here is the arithmetic for 1,000 cold emails a day:

On adbtd that setup costs $105.66 a month (34 mailboxes + 2 IPs), plus whatever your registrar charges for the 12 domains. Add follow-ups to the daily count: a three-step sequence to 1,000 new people a day settles at several times that volume.

The point of the exercise is the direction of scaling. When you need more volume, add mailboxes and domains. Raising the per-mailbox number is the fastest way to turn a healthy setup into a spam-folder one.

Per-mailbox sending limits

There are two different numbers people call “the limit”, and confusing them is a common mistake.

• Platform limits are hard caps the provider enforces. Google Workspace, for example, allows 2,000 messages per user per day (1,500 through mail merge), 2,000 external unique recipients a day, and locks sending for up to 24 hours once a limit is hit. These are designed for normal business mail and say nothing about what is safe for cold outreach.
• Reputation limits are what receivers will tolerate from an address before engagement drops and filtering kicks in. For cold email the common working number is around 30 new messages per mailbox per day, which is also what cold-email vendors like Infraforge and Mailforge recommend in their own setup guides.

On a dedicated stack such as adbtd there is no platform cap at all: the IP is yours and so is the reputation. That is freedom, not permission. Our docs publish a recommended ramp, and the dashboard shows Google Postmaster and Microsoft SNDS data so you can see when a receiver starts to disagree with your volume.

Warmup

A new domain, mailbox or IP has no reputation. Receivers treat a stranger that suddenly sends hundreds of messages a day the same way they treat a spammer cycling through fresh addresses, so you ramp volume gradually and let positive signals (delivered, opened, replied to, not reported) accumulate first.

A conservative ramp. Slow down if bounces or complaints rise; a new dedicated IP may need longer than a new mailbox on an established one.

There are two ways to generate early, positive traffic. Warmup networks are tools that connect your mailbox to a pool of other mailboxes that open, reply to and rescue each other’s messages from spam. Organic warmup means starting with the people most likely to engage: existing customers, partners, warm leads. Most teams combine both. Warmup tools connect over SMTP and IMAP, so they work with any provider that gives you those credentials, adbtd included; we do not run a warmup network ourselves.

The Google, Yahoo and Microsoft sender rules

The three largest consumer mailbox providers now publish explicit requirements. They overlap heavily: authenticate with SPF and DKIM, publish DMARC, align the From domain, keep complaints low, and make unsubscribing easy.

Summarised from Google’s email sender guidelines and FAQ, Yahoo’s sender best practices and Microsoft’s Outlook.com high-volume sender requirements, as published in October 2026.

Three details that matter for cold email specifically:

• The thresholds are about receivers, not you. Google’s 5,000-a-day line counts messages to personal Gmail accounts, and its guidelines say they do not apply to mail sent to Google Workspace accounts. Most B2B prospects are on Workspace or Microsoft 365, whose own filters judge you on the same signals anyway. Treat the bulk rules as the baseline for every domain.
• Alignment is what DMARC actually checks. SPF passing for your provider’s bounce domain is not enough; the domain in the visible From address has to match the SPF or DKIM domain. A dedicated setup that signs with your own domain and uses your own return-path passes this by design.
• Unsubscribe still matters. Google requires one-click unsubscribe only for marketing and subscribed mail, but cold outreach is promotional by nature, and an easy opt-out is cheaper than a spam complaint. Include a plain-language opt-out line, and a List-Unsubscribe header if your sending tool supports it.

The setup checklist

1. Register two to three secondary domains per ten mailboxes you plan, and redirect their websites to your main site.
2. Publish SPF (ending in -all or ~all, under ten DNS lookups), a 2048-bit DKIM key, DMARC with a rua= reporting address, and an MX record. Add MTA-STS and TLS-RPT if your provider supports them.
3. Check that your sending IP has a PTR record whose hostname resolves back to the same IP.
4. Create mailboxes with real names and set up signatures and profile details.
5. Send a real message from each new domain to check.adbtd.com, a free deliverability test, and fix everything it flags before you warm up.
6. Connect the mailboxes to your sequencer and warmup tool over SMTP / IMAP and ramp for two to four weeks.
7. Register your domains with Google Postmaster Tools and your IPs with Microsoft SNDS, and watch spam rate and reputation weekly.
8. Once reports show all legitimate mail passes DMARC, move from p=none to p=quarantine.
9. Scale by adding mailboxes and domains, never by raising per-mailbox volume.

Where adbtd fits

adbtd gives each customer their own Postfix and Dovecot stack on at least one dedicated IP, with SPF, DKIM, DMARC, MTA-STS, TLS-RPT and BIMI records generated for every domain and audited every six hours. You bring the domains from any registrar, pay $1.99 per mailbox and $19 per dedicated IP a month, and connect any sequencer or warmup tool over SMTP and IMAP. There are no sending caps and no warmup network: you own the reputation, and the dashboard shows you how it is doing.

If you are weighing it against the mailbox resellers, we wrote honest comparisons with Google Workspace, Zapmail, Mailforge, Infraforge and Maildoso, including when each of them is the better choice.

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