Google Workspace vs Microsoft 365: MX Records of 696 Companies

SaaS companies run their email on Google; large enterprises run theirs on Microsoft behind a security gateway. In MX records we looked up on 2 October 2026, 93.5% of 200 SaaS companies received mail directly at Google Workspace. Among 496 S&P 500 companies, only 4.0% did, while 45.2% routed mail through Proofpoint and 29.0% straight to Microsoft 365.

If you send B2B email, that split decides how your messages are filtered and how verification behaves on each side. Here is the data and what it means.

Method

We read MX records, the DNS entries that tell the world where a domain's mail goes. They are public, so anyone can repeat this.

Two samples:

• S&P 500 (496 domains). Constituents from Wikipedia's "List of S&P 500 companies", with each company's official website domain from Wikidata. Duplicate domains (such as Alphabet's two share classes) were merged and three companies with no recorded website were left out.
• SaaS (200 domains). The 200 largest companies by listed team size among those tagged SaaS in Y Combinator's public directory (B2B, active or public), via the open mirror at yc-oss.github.io.

We queried MX, plus the apex TXT records for SPF, using dnspython against 1.1.1.1, 8.8.8.8 and 9.9.9.9 at 03:38 UTC on 2 October 2026. Each domain was classified by its primary MX host, the one with the lowest preference number. We did not open SMTP connections.

The headline: two different worlds

SaaS is a Google market. The S&P 500 is a gateway-and-Microsoft market.

Primary MX host	SaaS (n=200)	Share	S&P 500 (n=496)	Share
Google Workspace	187	93.5%	20	4.0%
Microsoft 365	5	2.5%	144	29.0%
Proofpoint	1	0.5%	224	45.2%
Mimecast	1	0.5%	27	5.4%
Cisco Secure Email	0	0%	25	5.0%
Own servers (MX on own domain)	0	0%	20	4.0%
Other providers	3	1.5%	16	3.2%
No MX record on this domain	3	1.5%	20	4.0%

"Other" in the S&P 500 covers Trellix (2), CSC (2), and one each of Zoho Mail, GoDaddy, Cloudflare Email Security, Broadcom (Symantec) and Trend Micro, plus 7 hosts we could not attribute to a named provider.

Classification rules, so you can check them: Google if the host ends in google.com, googlemail.com or smtp.goog; Microsoft if it ends in protection.outlook.com, protection.office365.us, outlook.com or messaging.microsoft.com; Proofpoint for pphosted.com and gpphosted.com; Mimecast for mimecast.com; Cisco for iphmx.com.

The gateway problem: MX hides the mailbox provider

Over half of S&P 500 domains (281, or 56.7%) route mail through a security gateway first. Proofpoint, Mimecast, Cisco and the smaller filtering services accept the connection, scan the message and pass it on. The MX record tells you about the filter, not where the mailbox lives.

To see behind the gateway we used the SPF record, which lists the services allowed to send as the domain. A company whose staff send from Microsoft 365 has to include spf.protection.outlook.com; one on Google Workspace includes _spf.google.com.

Inferred mailbox provider, S&P 500	Domains	Share
Microsoft 365, MX points straight at it	144	29.0%
Microsoft 365, gateway in front, SPF includes Microsoft	69	13.9%
Google Workspace, MX points straight at it	20	4.0%
Google Workspace, gateway in front, SPF includes Google	4	0.8%
Both Microsoft and Google in SPF	1	0.2%
Gateway or other host, no provider in SPF	238	48.0%
No MX on this domain	20	4.0%

That gives a floor: at least 213 S&P 500 companies (42.9%) use Microsoft 365 and 24 (4.8%) use Google Workspace, on direct evidence.

Of the 238 unresolved domains, 177 sit behind Proofpoint, and 138 use SPF macros, which we explain in our SPF study. Proofpoint's hosted SPF, for one, replaces the provider list with a single dynamic include, so it no longer shows which mailbox provider sits behind it.

There is one more, weaker clue. When a domain is added to a Microsoft 365 tenant, Microsoft asks for a verification TXT record beginning MS=. 162 of those 238 domains still carry one. That proves the domain was connected to a Microsoft tenant at some point; it does not prove mail is delivered there today. Read it as "Microsoft very likely", not as a count.

Put plainly, Microsoft 365 is the mailbox provider for somewhere between 43% and 76% of the S&P 500 in this sample, and Google is under 5%. The SaaS sample is almost the mirror image.

Why SaaS is different

The data does not tell us why, and we will not invent a survey. The observable facts are these: the SaaS companies in the sample are younger (they went through YC between 2008 and 2025), smaller (the 200th company lists 24 staff) and, by their SPF records, heavy users of tools that integrate with Google. 88.3% of their SPF records include _spf.google.com. Only one SaaS company routes mail through Proofpoint and one through Mimecast.

What this means for B2B senders

Your mail to a startup and your mail to an enterprise are judged by different systems. Three practical consequences:

1. Verification results differ by recipient type

When a verifier asks Google's mail servers whether someone@startup.com exists, Google answers definitively for most addresses. That is why SaaS-heavy lists verify cleanly.

Gateways can behave differently. Some are configured to accept every recipient at the connection stage and only reject later, after looking the address up internally. To a verifier that looks like a catch-all domain: every address appears to be accepted, so none can be confirmed. An honest verifier returns those as risky rather than valid. Expect a much larger risky share on lists of enterprise contacts, and see what a catch-all domain is for how to handle them.

2. Filtering happens twice at large companies

A message to a Proofpoint-fronted Microsoft 365 domain passes the gateway's filters and then Microsoft's. Authentication matters at both. Make sure your own domain's SPF, DKIM and DMARC are in order before an enterprise campaign; the deliverability check covers all three.

3. Provider guidance applies by recipient

For SaaS recipients, Google's sender guidelines are what count. For enterprise recipients, Microsoft's outbound requirements and the gateway's reputation systems do. Our posts on Gmail and Yahoo's bulk sender requirements and Microsoft's requirements cover each side.

Check any company yourself

Two DNS queries answer most cases:

dig +short MX example.com
dig +short TXT example.com | grep spf1

If the MX host ends in...	Then...
google.com, googlemail.com	Google Workspace
mail.protection.outlook.com	Microsoft 365
pphosted.com	Proofpoint gateway, so check SPF
mimecast.com	Mimecast gateway, so check SPF
iphmx.com	Cisco Secure Email gateway, so check SPF

Or use the MX lookup tool, which shows the hosts and preferences in a browser.

Limitations

• Website domain, not necessarily mail domain. We used each company's official website domain as recorded in Wikidata. A few large companies use a different domain for staff email (for example, a corporate-site domain with no MX at all), which is why 20 S&P 500 domains had no MX record. We did not go looking for the "real" mail domain, to avoid choosing it by hand.
• SPF inference is a floor. A domain can include Microsoft in SPF for one application while hosting mailboxes elsewhere. A domain whose SPF uses macros hides its provider entirely.
• Primary MX only. We classified by the lowest-preference host. Backup MX hosts were recorded in the raw data but not used.
• Not a market-share survey. These are two samples of large, well-known companies. Small businesses, and companies outside the US, will look different.
• One snapshot, taken on 2 October 2026.

The short version

• 93.5% of 200 SaaS companies receive mail directly at Google Workspace.
• Only 4.0% of 496 S&P 500 companies do. 45.2% use Proofpoint as their front door, and 29.0% point MX straight at Microsoft 365.
• Behind the gateways, SPF shows Microsoft 365 for at least 42.9% of the S&P 500 in total.
• Gateways make many enterprise domains look catch-all to a verifier, so expect more risky results on enterprise lists.

Raw data: download the full dataset as CSV. It is free to reuse with a link back to this page.