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Best cold email infrastructure (2026): mailboxes, domains, and how to set them up

Cold email infrastructure is the domains and mailboxes you send from. Serious senders never use their main company domain. They buy a set of secondary domains, put a few mailboxes on each, set up SPF, DKIM, and DMARC, warm them, and spread volume across all of them.

Doing that by hand in Google Workspace or Microsoft 365 is slow and easy to get wrong, so a set of providers now does it for you. Below is what OneGTM uses for client sending, then the other providers worth knowing, with what each costs. Some links are referral links that may earn us a credit, which never changes what you pay or who is listed.

By Garrett Wolfe, founder of OneGTM (Clay Artisan Solutions Partner) and former GTM engineer at Unify. Updated .

Key takeaways

  • Send cold email from secondary domains, with two or three mailboxes per domain.
  • Google Workspace inboxes cost more and tend to land best with Google recipients. Microsoft and SMTP are cheaper per inbox.
  • Our setup is ScaledMail for mailboxes and domains, then warmup and sending in Instantly.
  • Infrastructure providers set up DNS, but you still need warmup, verified lists, and low volume per mailbox.

What OneGTM uses

We keep infrastructure separate from sending. ScaledMail provides the domains and mailboxes, and Instantly warms them and runs campaigns. Every domain goes through our deliverability checker before it sends.

ScaledMail

OneGTM uses this

Sets up and manages Google Workspace, Microsoft 365, and SMTP mailboxes for cold email, including domains and SPF, DKIM, and DMARC. It does not warm mailboxes, so we pair it with Instantly.

Best for: Mixed Google, Microsoft, and SMTP infrastructure at scale

Pricing: Google Workspace $3.50 per mailbox per month; Microsoft $50 per domain per month for 25 mailboxes; SMTP $3.75 per domain per month for 4 mailboxes. Domains extra.

Instantly

OneGTM uses this

Our cold email platform, with unlimited warmup on every plan. It also sells done-for-you Google accounts and pre-warmed accounts that plug straight into campaigns.

Best for: Buying mailboxes and sending in one place

Pricing: Done-for-you Google account $5/month; Airmail account $4/month; pre-warmed Google account $10/month; domains $15/year. Requires an Outreach plan, from $47/month.

Google Workspace and Microsoft 365 inbox providers

These resell or provision real Google and Microsoft mailboxes, configure DNS automatically, and connect them to your sequencer.

InboxKit

Google Workspace and Microsoft 365 mailboxes with automated DNS, an admin panel per domain, monitoring, and connections to 24+ sequencers. Optional warmup and blacklist monitoring add-ons.

Best for: Pay-per-mailbox Google or Microsoft with no minimums

Pricing: Google or Microsoft $3/mailbox/month, or $2.50 billed yearly. Azure tenants $30/month for up to 100 mailboxes. No minimums.

Zapmail

Google and Microsoft mailboxes under one plan, with instant SPF, DKIM, DMARC, and tracking domain setup, plus deliverability tests. Also powers some of Smartlead's SmartSenders options.

Best for: Small teams that want a bundle of mailboxes

Pricing: Starter $39/month for 10 mailboxes; Growth $99/month for 30; Pro $299/month for 100. Extra mailboxes $3 to $3.50.

Hypertide

Google inboxes and Microsoft Entra domains with automated deployment, reply relay, and upload to sequencers by OAuth or SMTP.

Best for: Cheap Microsoft inboxes at volume

Pricing: Google $3.30 per inbox per month, no minimums; Microsoft $25 per domain per month including 25 inboxes.

Cheap Inboxes

Google Workspace and Microsoft mailboxes at the same price, with DNS, forwarding, domain masking, and export to Instantly, Smartlead, or lemlist.

Best for: Volume discounts on Google inboxes

Pricing: $3.50 per mailbox per month for 1 to 99, down to $2.80 at 1,000+. Domains from $2.50/year.

Smartlead SmartSenders

Smartlead's built-in mailbox store. Buy Google, Outlook, or SMTP mailboxes from partner providers inside Smartlead, fresh or pre-warmed.

Best for: Smartlead users who want one bill

Pricing: Fresh Google or Outlook $4.50/mailbox/month plus $13/domain/year; pre-warmed $9/mailbox/month plus $18/domain/year; SMTP from $3.99. Smartlead Base from $39/month.

SMTP and private infrastructure

These run their own mail servers and IPs instead of Google or Microsoft. Much cheaper per mailbox, and reputation depends on how well the provider manages its IPs.

Mailforge

Low-cost mailboxes on a shared IP pool, with automated DNS setup.

Best for: Budget mailboxes for high volume

Pricing: $3 per mailbox slot per month ($2.40 billed yearly), minimum 10 slots; .com domains $14/year.

Infraforge

Mailforge's private option, on dedicated servers with optional dedicated IPs, so other senders cannot affect your reputation.

Best for: Teams that want isolated IPs

Pricing: $4 per mailbox slot per month, minimum 10 slots; dedicated IP $99/month; .com domains $14/year.

Maildoso

SMTP mailboxes on Maildoso's own servers and IPs, with IP rotation. Warmup is not included, so it pairs with a tool like Instantly.

Best for: The lowest cost per mailbox

Pricing: $75/month for 30 mailboxes; $225/month for 300; $499/month for 1,000. Domains $12/year ($15 from October 1, 2026) or bring your own.

Mailreef

Dedicated mail server and dedicated IP with 150+ mailboxes per server, automatic DNS, and pre-warmed options. Recommends at most 3 mailboxes per domain.

Best for: Agencies sending high volume on their own server

Pricing: Agency $240/month on a 12-month term or $249/month month to month, plus $0.001 per send. Enterprise custom.

Prices are from each vendor's site as of October 2026 and change often, so check before you buy. This is an opinionated list, not a paid ranking. Some links are referral links that may earn us a credit; that never changes what you pay or who makes the list.

Cold email infrastructure compared

ToolBest forStarting price
ScaledMail (OneGTM uses)Mixed Google, Microsoft, and SMTP infrastructure at scaleGoogle $3.50 per mailbox per month
Instantly (OneGTM uses)Buying mailboxes and sending in one placeDFY Google account $5/month
InboxKitPay-per-mailbox Google or Microsoft with no minimums$3 per mailbox per month
ZapmailSmall teams that want a bundle of mailboxesStarter $39/month for 10 mailboxes
HypertideCheap Microsoft inboxes at volumeGoogle $3.30 per inbox per month
Cheap InboxesVolume discounts on Google inboxes$3.50 per mailbox per month
Smartlead SmartSendersSmartlead users who want one bill$4.50 per mailbox per month
MailforgeBudget mailboxes for high volume$3 per mailbox per month
InfraforgeTeams that want isolated IPs$4 per mailbox per month
MaildosoThe lowest cost per mailbox$75/month for 30 mailboxes
MailreefAgencies sending high volume on their own server$249/month plus $0.001 per send

Starting prices as published by each vendor in October 2026.

Google vs Microsoft vs SMTP

Google Workspace inboxes cost the most per mailbox and are the common default, partly because mail from Google tends to be treated well by Google recipients. Microsoft 365 is sold by these providers in tenant or domain bundles, so the cost per inbox drops sharply, and it tends to suit lists heavy on Outlook users. SMTP and private servers are the cheapest and give you the most control, but your results depend on the provider's IP reputation.

Many teams mix them: Google for the main audience, Microsoft for Outlook-heavy lists or extra volume, and SMTP for testing or large, lower-value sends. Check what your list's domains actually use before you decide. An MX lookup tells you whether a prospect's company is on Google or Microsoft.

  • Google Workspace: about $3 to $5 per mailbox per month with these providers.
  • Microsoft 365: about $0.30 to $2 per mailbox when bought as a domain or tenant bundle.
  • SMTP: under $1 to about $4 per mailbox, depending on volume and dedicated IPs.

How many domains and mailboxes you need

Work back from daily volume. Decide how many cold emails each mailbox will send a day, divide your target volume by that to get the mailbox count, then divide by two or three mailboxes per domain. Smartlead limits SmartSenders domains to three mailboxes, and Mailreef recommends at most three per domain and 50 emails per mailbox per day, which are sensible ceilings. Lower is safer.

Buy domains that look like your brand (a .com with a small variation, not a random string), point them at your main site, and set SPF, DKIM, and DMARC on each one. Every provider here automates those records. Check them yourself anyway with our deliverability checker, because one missing DKIM record can sink a whole domain.

Handing off to warmup

Most infrastructure providers stop at working mailboxes. Connect them to your sending platform, turn on warmup, and wait about two weeks before campaigns start. Keep warmup running at a lower level afterward. Pre-warmed accounts skip part of the wait but cost about twice as much and still need a slow ramp.

Our email warmup tools guide covers the warmup side, and cold email software covers the sequencers these mailboxes plug into.

When to get help

Buying mailboxes takes ten minutes. The expensive mistakes come from sending too much per mailbox, skipping DMARC, sending from the main domain, and nobody watching placement until replies stop.

OneGTM sets up domains, mailboxes, DNS, and warmup, then runs campaigns with volume kept inside safe limits. You own every domain and mailbox.

  • You are launching cold email and want the infrastructure right on day one.
  • You need to go from a handful of mailboxes to dozens without burning domains.
  • Reply rates dropped and you suspect your mailboxes are landing in spam.

Book an infrastructure review

Cold email infrastructure FAQ

What is cold email infrastructure?
It is the secondary domains, mailboxes, and DNS records you send cold email from, kept separate from your main company domain so cold outreach cannot damage it. Providers like ScaledMail, InboxKit, and Zapmail set it up for you.
Should I use Google Workspace or Microsoft 365 for cold email?
Google Workspace is the common default and tends to land well with Google recipients. Microsoft is far cheaper per inbox through these providers and can suit Outlook-heavy lists. Many teams use both and route by the prospect's email provider.
How many mailboxes per domain should I use?
Two or three. More mailboxes on one domain concentrates risk, and Smartlead and Mailreef both cap or recommend a maximum of three. Add domains to grow volume instead of adding mailboxes to the same domain.
How many cold emails can one mailbox send a day?
Keep it low. Mailreef recommends no more than 50 per mailbox per day, and many teams send fewer. Scale by adding mailboxes and domains rather than pushing each mailbox harder.
Do infrastructure providers include warmup?
Usually not by default. ScaledMail and Maildoso do not warm mailboxes, and InboxKit sells warmup as an add-on. Most teams warm mailboxes in their sending platform, such as Instantly or Smartlead, for about two weeks before campaigns start.
Are SMTP mailboxes good for cold email?
They can be, and they are the cheapest option. Results depend on the provider's IP reputation and whether you share IPs with other senders. Dedicated IPs, such as Infraforge or Mailreef offer, remove the risk of other senders hurting you.
Do I own the domains?
Check before you buy. Most providers let you bring your own domains or transfer purchased ones out, and some pre-warmed offerings keep admin access. If you work with OneGTM, the domains and mailboxes are yours.

Want cold email infrastructure that is set up right from the first send?

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