Mailbox Types · Selector
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 why SMTP is not on the menu.
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.
Why we do not sell SMTP
SMTP relays are the fastest thing to deploy: you can be sending in minutes instead of waiting on provisioning. That speed is the whole pitch, and it is also the problem. Deliverability depends entirely on the reputation of the underlying servers and IPs, which you do not control and usually cannot inspect. On clean infrastructure it performs. On the cheap, recycled IPs most resellers run, it collapses, and you find out after you have burned a list.
We sell Azure and Google because both give you mailboxes on infrastructure with a reputation you can build and keep. If you do buy SMTP elsewhere, ask who owns the IPs, how many other senders share them, and what happens to your sending when one of them gets blacklisted.
Azure or Google, side by side
| Microsoft Azure | Google Workspace |
|---|---|
| High (esp. Outlook) | Highest |
| Lowest | Higher |
| Yes (.com) | No |
| 2 to 3 | Up to 15 |
| Volume at low cost | Quality outreach |
Frostmailer pricing as of 2026: Azure from €0.30 per account per month with the .com domain included (tenants of 25, 50 or 100), Google full admin from €3.00 per inbox (€2.50 at 500+, 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.