Cold email infrastructure definition

Most plans price the tool and forget what sits under it. Below: what the infrastructure consists of, how many domains and mailboxes a volume target needs, what standards say about lookalike domains, what custom SMTP changes, and what the infrastructure costs before any tool is added.

What is cold email infrastructure?

It is the sending side of outreach, in five parts.

• Sending domains: domains used only for outreach, kept apart from the main company domain.
• Mailboxes: real accounts on Google Workspace, Microsoft 365 or another provider, each under a person's name.
• DNS records: SPF, DKIM and DMARC on every sending domain.
• Connection: the link between the mailboxes and the sending tool, through an official connector or custom SMTP.
• Rotation: the rule that spreads sends across mailboxes and domains.

The main company domain stays outside this set. If it has years of reputation behind it, cold outreach puts that reputation at risk for day-to-day business mail. Leadspicker recommends a separate set of domains bought for the purpose.

M3AAWG's Sending Domains Best Common Practices recommend subdomains per sending purpose and strongly discourage cousin domains. M3AAWG's Sender Best Common Practices v4.0 (August 2026) repeats that advice and describes a warm-up of about six weeks. Spamhaus's sender guidelines advise against sending from a new domain for 30 days and warn that warm-up services can lead to a listing. Provider caps are set in Google Workspace's sending limits and Microsoft's Exchange Online limits.

How many domains and mailboxes does a volume target need?

Work backwards from the per-mailbox limit. Leadspicker's guidance is 5 cold emails per mailbox per day and 2 to 3 mailboxes per domain. Volume grows by adding mailboxes and domains, not by pushing one mailbox harder, because reputation lives at the domain level.

Assumes about 20 sending days a month, 5 cold emails per mailbox per day and 3 mailboxes per domain, all Leadspicker guidance pending clearance. The 3,000 row is Leadspicker's worked example for a target of 20 to 30 meetings a month. The last row is Leadspicker's description, not a calculation.

Lookalike domains or subdomains: what do standards say?

Standards and cold-email practice disagree here. M3AAWG's Sending Domains best practices recommend subdomains of the main domain for each sending purpose and call cousin, or lookalike, domains strongly discouraged. Its Sender Best Common Practices v4.0, published in August 2026, repeats the advice to avoid lookalike domains and describes a warm-up of about six weeks. Cold-email practice usually sends from separate lookalike domains so that a reputation problem cannot reach the main domain. Leadspicker recommends the same.

Spamhaus adds a timing rule: do not send from a newly registered domain for its first 30 days, and do not use warm-up services, which it treats as grounds for listing. Most cold-email setups start sooner. If you follow that practice, know that it contradicts a blocklist operator that many receivers query.

What does custom SMTP change?

Custom SMTP connects almost any mailbox to a sending tool, and the cost is visibility. With an official Gmail or Outlook connector the tool works through the provider's own interface and can match the sending provider to the recipient's. Over custom SMTP it sees a server address and a password.

In Leadspicker's support experience, custom SMTP with missing authentication is the single most common cause of 'sending but no results', and the platform cannot warn about it because it has no view of the domain's configuration. Treat custom SMTP as bring-your-own infrastructure: the DNS checks, provider limits and reputation are yours.

Provider caps apply either way. Google Workspace sets per-user sending limits, lower on trial accounts. Microsoft's Exchange Online applies a tenant-wide limit on external recipients and points bulk senders to Azure Communication Services. Both are ceilings set by the provider, not targets for cold email.

What does infrastructure cost before any tool?

At 20,000 to 30,000 leads a month, Leadspicker estimates the infrastructure alone at high hundreds to low thousands of euros per month, before tooling and before anyone's time. It is an estimate, not a measurement, and it is the cost most plans leave out.

Below that scale, the cost follows the counts in the table above: each domain is a yearly registration and each mailbox a monthly seat with its provider. Price both from your registrar's and provider's current lists, because both change.

Leadspicker's view is that high volume makes sense in one situation: entering a new market with no signal about who converts. Elsewhere, fewer and more relevant contacts need less infrastructure. Going too small fails too: Leadspicker's guidance is that at 100 emails a month there is no readable result.

Frequently asked questions

How many mailboxes do I need for cold email?

Divide your daily send target by a conservative per-mailbox volume, then spread the mailboxes across several domains so no single domain carries the load. The volume table on this page shows the arithmetic for three targets.

Should I use a lookalike domain or a subdomain?

M3AAWG recommends subdomains and strongly discourages lookalike domains. Cold-email practice often uses lookalikes to keep problems away from the main domain; weigh that protection against the standards and the impersonation risk.

Is custom SMTP safe for cold email?

It works, but the sending tool cannot see your DNS. If SPF, DKIM or DMARC is missing, reputation erodes without a warning, so check every record yourself before the first send.