Short answer: for cold emailing, Microsoft 365 is my default recommendation, Google Workspace is a close second, and raw SMTP inboxes are last by a distance. That order surprises people because Google is the bigger name. But in my sending, Microsoft inboxes outlast Google ones, they survive longer at the same volume, and they complain less. Google still sends well when everything is set up right. SMTP is cheap for a reason, and the reason is where your mail lands.
I have run cold outreach across all three for years, for my own campaigns and for client infrastructure I built and managed. What follows is not a spec sheet comparison. It is what each provider actually does to you when you send cold email through it week after week.
Which email provider is best for cold emailing, honestly?
The provider decides your infrastructure ceiling. Receivers know which network your mail comes from and they treat that traffic as a group before they ever look at your individual domain. That shared reputation is the thing you are really renting.
Microsoft 365 sends from a network that B2B receivers trust, because most of the corporate world runs on it. Your cold email arrives from the same neighborhood as ordinary business mail. Google Workspace has strong trust too, but Google is also the strictest landlord in the business when it decides you are a bulk sender, and Workspace inboxes built purely for outreach tend to get flagged faster in my experience. SMTP servers, the kind sold cheap by inbox resellers, send from IP ranges that filters have seen a thousand times. The welcome is colder from the first email.
None of this rescues a bad setup. A Microsoft inbox with broken authentication and a dirty list dies just as dead as any other. But when two senders do everything else equally, the provider is the difference I keep seeing.
Google Workspace for cold email
Workspace is the provider most cold email content is written about, and it is genuinely good. Deliverability on a properly authenticated Workspace domain is strong, the admin console is familiar to everyone, and DKIM setup is a few clicks once you know where to look.
Where it bites people: Google knows exactly what fresh outreach setups look like, because it watches billions of messages. New Workspace tenants sending cold volume get scrutinized early. Inbox lifespan can be short if you ramp carelessly, and Workspace accounts bought through resellers of varying honesty add another way to get shut down. The authentication side is easy to verify though. A Workspace domain should publish the Google SPF include and a Google DKIM key, and you can confirm both in a minute with an SPF checker for Google Workspace.
Best for: senders who want the most documented setup path, teams already living in Google, and anyone whose prospects are mostly other Google shops.
Microsoft 365 for cold email
This is where I build first when a client gives me the choice. In my sending, Microsoft inboxes outlast Google ones at comparable volume, and deliverability into corporate inboxes, which is most of B2B, is consistently a touch better. The tenants feel less twitchy. You set up your domains, publish your records, warm up like an adult, and it just sends.
The friction is real but smaller than people claim. The admin side is more enterprise flavored, DKIM lives in the Defender portal rather than somewhere friendly, and selector setup confuses first timers. It is a one time annoyance. You publish selector1 and selector2 CNAMEs, turn DKIM on for the domain, and a DKIM checker for Microsoft 365 will tell you whether both selectors actually resolve. Half the "Microsoft deliverability problems" I get asked about turn out to be DKIM that was enabled in the portal but never published in DNS.
Best for: B2B senders whose prospects sit in corporate Microsoft environments, and anyone who wants inbox lifespan over setup convenience.
The truth about cheap SMTP inboxes
SMTP inboxes get sold on price. A dollar or two per inbox, hundreds of inboxes ready tomorrow, no Workspace or Microsoft account hassle. It sounds like arbitrage. It is usually a slow way to burn domains.
In my experience, mail from bargain SMTP setups lands in spam at rates the other two providers never produce, even with identical domains, authentication, and copy. The IPs and sending patterns of those networks are known to filters. You are sharing a reputation pool with every other budget sender who bought the same deal, including the ones blasting scraped lists at full volume. Their behavior becomes your deliverability.
Is there any case for it? Testing throwaway ideas on domains you do not care about, maybe. For a client, for your agency, for anything with your name on it, no. The money you save on inboxes gets spent several times over on replacement domains and lost weeks.
Before you blame any provider, though, run the basics: SPF, DKIM, and DMARC either pass or they do not, and an email authentication checker will show you the truth for any domain in about a minute. Provider choice sits on top of authentication, never instead of it.
If you are X, buy Y
- You sell to corporate and enterprise prospects: Microsoft 365. Your mail comes from their own neighborhood.
- You are a solo sender or small agency and want the smoothest learning curve: Google Workspace, accepting somewhat shorter inbox life.
- You are building client infrastructure that has to survive month after month: Microsoft 365 as the base, Workspace mixed in if you want provider diversity across domain groups.
- You are tempted by the cheapest inbox deal you found in a Discord server: stop. Buy ten proper inboxes instead of a hundred SMTP ones and keep your domains alive.
- You already own one of them and it is set up correctly: keep it. A well run Workspace setup beats a sloppy Microsoft one every day of the week.
The provider is only part of the outcome
Here is the part the provider wars leave out. I would put the provider at maybe 20 percent of your results. The rest is the boring stack: secondary domains you are willing to protect, authentication that actually passes, warm up with patience, verified lists, and copy that does not read like a template. I have watched senders blame Google while their DMARC pointed nowhere and their list was 15 percent dead addresses. No provider on earth fixes that.
Pick Microsoft if you want my default. Pick Google if your world already runs on it. Either way, build the infrastructure properly or have it built. That is most of what our cold email infrastructure builds do for clients, and it matters more than which logo is on the inbox.
Frequently asked questions
Is Google Workspace or Microsoft 365 better for cold email?
For pure cold outreach, Microsoft 365 is my default. In my sending its inboxes last longer and land well with corporate receivers. Google Workspace sends well too and has the easier setup. The gap is real but smaller than the gap between a good setup and a bad one.
Can I use my regular company inbox for cold email?
Do not. Cold outreach belongs on secondary domains with their own inboxes, whoever the provider is. One spam complaint spiral on your main domain can damage the mail your whole company depends on, invoices and client emails included.
Are cheap SMTP inboxes worth it for cold emailing?
In my experience, no. They are cheap because the sending reputation is poor, and your mail lands in spam at rates that eat whatever you saved. They can be fine for throwaway testing. For real campaigns they cost you domains.
How many inboxes do I need per domain?
A handful. I run a few inboxes per secondary domain and keep per inbox daily volume at a level a busy human might send. Dozens of inboxes on one young domain looks like exactly what it is, and filters treat it that way.