Key takeaway: For cold email, the two mailboxes worth running are Microsoft Azure for cost efficient volume and Google Workspace for the highest quality placement. Both should arrive pre-warmed. SMTP is a niche speed play, not the default.

The first real decision in cold email infrastructure is what kind of mailbox you send from. At Frostmailer we push two: Microsoft Azure and Google Workspace, both pre-warmed. Here is how they differ and where SMTP fits.

Microsoft Azure (Microsoft 365)

Azure is the value play and the one most agencies scale on. You can stand up a tenant with a large block of mailboxes for a fraction of Google's per inbox cost, which transforms the economics at scale, and Microsoft inboxes land well with other Outlook recipients, a big share of B2B. Because per inbox sending stays deliberately low, you lean on breadth: many inboxes, a few sends each. We recommend 2 to 3 emails per inbox per day, on a two week warm-up. The .com domain is included. Best for high volume at low cost per lead.

Google Workspace

Google has the strongest reputation in the business. Its infrastructure is trusted almost everywhere, so well managed accounts see top tier placement. The trade-off is a higher cost per inbox, and Google keeps daily sends low to protect reputation. We recommend up to 15 emails per inbox per day, on a two week warm-up. The domain is not included. Best for quality focused outreach where a reply is worth a lot.

SMTP

SMTP is the most flexible and fastest to deploy: you can be sending in minutes instead of waiting on provisioning. The catch is that deliverability depends entirely on the quality of the underlying servers and IPs. On reputable infrastructure it performs; on cheap, abused IPs it falls apart. It is a niche option for speed on infrastructure you trust, not the default for most senders. The domain is not included.

Side by side

Frostmailer pricing as of 2026: Azure from €0.30 per account per month with the .com domain included (batches of 100), Google full admin from €3.00 per inbox (€2.50 at 500+, domain not included), SMTP from €1.20 per month (domain not included).

So which one?

For most senders the answer is Azure for cost efficient volume, with Google added for your highest value prospects. Run both through the same sending tool. The right split depends on your volume, your budget, and what an average reply is worth.

Whichever route you take, the make or break factor is the same: the infrastructure underneath has to be authenticated, warmed, and properly distributed. Frostmailer delivers Azure and Google mailboxes pre-warmed with that groundwork done, so you choose based on your campaign, not on what you can stomach setting up by hand.

Want this done for you?

Our Build and Release service stands up your entire cold email infrastructure: domains, mailboxes, authentication, warm-up, and tracking, all authenticated and ready to send. You skip the weeks of setup and start with campaigns.

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