What Microsoft's New-Tenant Sending Quotas Mean for Client Mailboxes

A new client signs. Their company moved to Microsoft 365 a few weeks ago, or they set up a fresh tenant for a new brand, and the plan is to start sending from those mailboxes in the first month. Nobody checks how old the tenant is, because until recently it did not matter much.

It matters now. Microsoft is rolling out lower outbound quotas for new and trial Exchange Online tenants between mid-September and the end of November 2026. For an agency, that means the mailbox you are about to connect may hit a hard ceiling that has nothing to do with your send caps, your warm-up plan, or the client's reputation.

Here is what changed, what did not, and a short check to run before you connect a client's Microsoft 365 mailboxes.

The limit that applies to the whole tenant

Exchange Online has a tenant-level outbound limit called the Tenant External Recipient Rate Limit, or TERRL. According to Microsoft's Exchange team, it is the maximum number of external recipients a tenant can send to in a 24-hour sliding window. An external recipient is anyone whose domain is not an accepted domain in the tenant, including people in other Microsoft 365 tenants.

For an established tenant, the quota is calculated from the number of email licenses:

500 × (licenses ^ 0.7) + 9,500

Microsoft's sample table puts that at 10,000 external recipients a day for a one-license tenant, about 12,000 for 10 licenses, and about 14,300 for 25.

Two details make this number smaller in practice than it looks:

• It is shared. Every mailbox in the tenant draws from the same quota. The client's finance team, support desk, and executives all count against it, not just the mailboxes you connect for outbound.
• It counts recipients, not people. Microsoft's FAQ says 1,000 messages to the same external address count as 1,000, and a message to a distribution group counts every expanded member.

What changed for new and trial tenants

Microsoft's message center notice MC1454397, updated September 29, 2026, says the rollout started in mid-September and should finish by the end of November 2026. Three groups are affected:

• New tenants. A tenant under 31 days old gets 10% of its standard quota. From 31 to 60 days it gets 25%. After 60 days it gets the full amount.
• Trial tenants. The daily quota drops from 5,000 to 500 external recipients, no matter how many licenses.
• Tenants with free education licenses. These get a new formula. That rarely matters for B2B outbound.

Run the math on a typical small client. A tenant with one to ten licenses has a standard quota of roughly 10,000 to 12,000. In its first month, that becomes roughly 1,000 to 1,200 external recipients a day for the whole company. In month two it is roughly 2,500 to 3,000.

When the tenant goes over, Microsoft blocks further external mail until the 24-hour total drops back under the limit. Senders get a bounce with code 550 5.7.233 for regular tenants or 550 5.7.232 for trial tenants.

What did not change

Two things are worth stating plainly, because older articles still describe them wrong.

First, the per-mailbox external limit of 2,000 recipients a day is not happening. Microsoft announced it in 2024, delayed it several times, and canceled it on January 6, 2026. The Exchange team's post says the per-mailbox Recipient Rate Limit and the tenant-level limit stay as they were. The Register's coverage notes that Microsoft said it would come back with "less disruptive" ways to deal with bulk sending, so expect more changes.

Second, none of this makes Exchange Online a bulk sending platform. Microsoft's post says Exchange Online does not support bulk or high-volume email outside its dedicated offering. A tenant quota is a ceiling, not a target. A client's outbound should sit far below it, with room left for the rest of the company's normal email.

A five-minute check before you connect a client's Microsoft 365 mailboxes

Add this to onboarding for every client whose mailboxes live in Exchange Online:

1. Ask how old the tenant is and whether it is a trial. If the client's IT contact does not know, the admin can look it up. A trial tenant at 500 external recipients a day is not ready for outbound at all.
2. Have the admin open the quota report. Microsoft points admins to the Exchange admin center under Reports > Mail flow > Tenant Outbound External Recipients Rate. It shows the current quota, how much has been used, and whether enforcement is on. The Get-LimitsEnforcementStatus cmdlet returns the same numbers.
3. Write down the normal daily volume. Before outbound starts, record how many external recipients the client's staff already sends to on a normal weekday. That is the floor your campaign sits on top of.
4. Set the campaign cap well inside the gap. Keep outbound to a small share of whatever is left. Warm-up schedules for new domains already start low, so a new tenant usually fits. The risk is a client who wants to "go big" in week one.
5. Route the bounce codes to a human. Add 5.7.233 and 5.7.232 to your bounce classification as "tenant quota," not "bad address." These are not list problems. Suppressing the recipients would be the wrong fix, and the next send would hit the same wall.

If a client is close to the quota on normal business email alone, that is a conversation to have before launch: the fix is a sending setup that fits the volume, not squeezing outbound into the margin.

Where GTM fits

GTM runs outbound for each client inside an isolated workspace, with send windows, sending limits, and the compliance gate set per client. A provider limit like this one belongs in the same place as the client's own caps, so the campaign stays well under the ceiling without anyone having to remember the tenant's age.

If you run outbound for several clients and want each one's limits enforced in its own workspace, join the waitlist.

Sources

• Microsoft Exchange Team, "Introducing Exchange Online Tenant Outbound Email Limits" (updated August 2026): https://techcommunity.microsoft.com/blog/exchange/introducing-exchange-online-tenant-outbound-email-limits/4372797
• Microsoft 365 Message Center MC1454397, "Updates to Tenant External Recipient Rate Limit (TERRL) Quotas for New, Trial, and Education Tenants" (archive): https://mc.merill.net/message/MC1454397
• Microsoft Exchange Team, "Exchange Online canceling the Mailbox External Recipient Rate Limit": https://techcommunity.microsoft.com/blog/exchange/exchange-online-canceling-the-mailbox-external-recipient-rate-limit/4483498
• Microsoft 365 Message Center MC787382, "Exchange Online to introduce External Recipient Rate Limit" (archive): https://mc.merill.net/message/MC787382
• The Register, "Microsoft scraps Exchange Online spam clamp after customers cry foul": https://www.theregister.com/security/2026/01/07/exchange-online-ditches-mailbox-recipient-rate-limit/5042244