Two thousand messages a day, and that is all

by Francis Rozange | Sep 8, 2026 | Email Marketing

Abstract 3D render: an upward funnel of light striking a hard glass ceiling, particles spilling

There is a conversation that happens every year in every company, and it always starts the same way: “how many can we send from our work mailbox?”

The answer is published. It is quantified. It is far lower than most people imagine, and at Microsoft it changes on 14 September 2026.

The warning to read first

Google opens its limits page with a sentence that is a commitment in reverse:

“Sending limits can change without notice. Limits per day are applied over a rolling 24-hour period, not a set time of day.”

Two pieces of information. Limits change without notice, so any architecture resting on an exact value is fragile. And the window slides: there is no reset at midnight. A mass send at 11 pm frees nothing at one minute past.

That is the first misunderstanding to clear up, and it regularly costs a full day of sending.

Google Workspace: two thousand, no more

For a paid account, the daily limit per user is 2,000 messages. It drops to 1,500 for a mail merge and 500 for a trial account.

The other ceilings are tighter than people think, because they count recipients rather than messages.

Recipients per message: 2,000 in total, of which at most 500 external. Total recipients per day: 10,000. External recipients per day: 3,000. Unique recipients per day: 3,000, of which 2,000 external.

A free Gmail account caps at 500 messages a day and 500 recipients per message. The gap with a business account is a factor of four, no more.

The penalty is described without ambiguity: “After reaching one of these limits, users can’t send new messages for up to 24 hours. However, they can still access their Google Workspace account, get incoming email, and use their other Google services.”

One billing detail, finally, that nobody reads and that explains many early-contract surprises: the limits of an account converted from a trial only rise after cumulative payments of at least 100 dollars, and “It can take up to 75 days after meeting this payment threshold for account sending limits to increase.”

The SMTP relay, and why it counts twice

Google’s SMTP relay is a different service, with different limits, and above all different counters.

Each user can relay 10,000 messages per 24 hours, to at most 10,000 unique recipients. At organisation level, the ceilings are 4.6 million non-unique recipients per 24 hours and 319,444 per ten-minute window.

Two technical rules deserve noting, because they break badly written integrations.

“There is a 100-recipient limit per SMTP transaction for smtp-relay.gmail.com. Exceeding this limit results in an error message. To send messages to additional recipients, start another transaction.”

And the counting rule, which is not intuitive: “The per-user recipient limits are for unique recipients. Per-account limits are for total recipients. For example, when a user relays 1,000 messages to Recipient-A and 1,000 messages to Recipient-B, it counts as 2 messages toward the per-user limit and 2,000 toward your account limit.”

Finally the point that settles the architecture: “The SMTP relay and Gmail user sending limits are independent and counted separately from each other.” The two counters do not talk to each other. An application going through the relay does not eat into the mailbox quota.

Microsoft 365: ten thousand, and a tenant ceiling

At Microsoft, the per-mailbox limit is 10,000 recipients per day, with a maximum rate of 30 messages per minute and a per-message recipient limit configurable from 1 to 1,000, defaulting to 500.

Microsoft closes the door on negotiation: “The recipient rate limit and message rate limit are hard limits enforced at the service level and can’t be increased.”

And it adds, in a note worth printing out for meeting rooms:

“Exchange Online customers who need to send legitimate bulk commercial email (for example, customer newsletters) should use third-party providers that specialize in these services.”

The vendor of your work email system is telling you not to do email marketing in it. That is not a consultant’s opinion, it is a note in its own documentation.

The tenant ceiling, and its formula

Since 2025 a second limit applies, at whole-organisation level: the Tenant External Recipient Rate Limit.

“The Tenant External Recipient Rate Limit (TERRL) is the maximum number of external recipients a tenant can send to per day (24-hour sliding window). External recipients are those whose email address domains aren’t an accepted domain in the tenant. This limit depends on the number of licenses a tenant has.”

The formula is published, and it is instructive:

500 × (number of licenses)^0.7 + 9,500

The 0.7 exponent means the ceiling grows more slowly than your headcount. One licence gives 10,000 external recipients a day. One hundred licences give 22,059, not a million. One thousand licences give 72,446.

In other words: buying licences to buy sending volume is a very poor calculation, and Microsoft has made that mathematically true.

Recent tenants are throttled further: 10 percent of the calculated quota for the first thirty days, 25 percent up to sixty days, 100 percent thereafter.

The associated rejections are documented: 550 5.7.232 for a trial tenant, 550 5.7.233 for the others. And a specific ceiling hits default domains: “Outbound mail from these domains is limited to 100 external recipients per organization within a 24-hour rolling window”, with code 550 5.7.236. One hundred external recipients a day for the whole organisation, if you send from your onmicrosoft.com domain.

What changes on 14 September 2026

Microsoft added an update to its original announcement on 13 August 2026:

“To further strengthen protection against abuse and ensure fair use of Exchange Online resources, we are updating how the Tenant External Recipient Rate Limit (TERRL) quota is calculated for certain tenants. These changes will begin rolling out starting September 14, 2026.”

The rollout also remains suspended for the GCC, GCC High, DoD and 21Vianet environments.

One inconsistency Microsoft has not resolved is worth flagging: for trial tenants, its blog announces 500 external recipients a day, its documentation pages announce 5,000. Two sources from the same vendor, two figures. We will not settle it on their behalf.

What to do tomorrow morning

Count what you actually send, over a rolling seven days, in external recipients rather than messages. That is the unit both operators count, and it is almost never the one internal dashboards track.

If you are approaching half of any ceiling, you do not have a volume problem: you have an architecture problem. A work email system is for correspondence, not for broadcasting, and both vendors say so in their own way.

If you are on Microsoft 365 and your external sending is significant, check your TERRL in the dedicated report in the admin centre before 14 September. The formula is changing for some tenants, and you would rather discover that in a report than in a 550 5.7.233.

And if you still send from an onmicrosoft.com domain, the hundred external recipients a day is not an incident to diagnose. It is the answer.

Sources

LaFactory works email on the evidence: headers, DNS records, rejection logs. No open rate promises, ever. Get in touch for a deliverability audit.