New Exchange Online Tenant Outbound Email Limits
What You Need to Know About TERRL
Exchange Online users! Big news from Microsoft: they’re rolling out a fresh set of rules to keep the email highways running smoothly.
Starting soon, Microsoft is introducing tenant-level outbound email limits called the Tenant External Recipient Rate Limit—or TERRL for short. If you’re an IT admin or just someone curious about how this affects your organization, stick around. We’re diving into what TERRL is, why it’s happening, and how you can stay ahead of the curve.
Why TERRL? Keeping the Spammers at Bay
Picture this: Exchange Online is like a bustling city street. Everyone’s zipping along, sending emails left and right. But every now and then, a few bad actors try to clog the roads with spam or misuse the system. To keep things flowing and ensure fair access for all, Microsoft is putting up some traffic lights—aka TERRL.
The goal? Reduce the risk of abuse and make sure Exchange Online stays reliable for legitimate users like you. TERRL caps how many external recipients (folks outside your organization’s domain) your tenant can email in a single day. Hit that limit, and further emails to outsiders get a polite “try again later” until your 24-hour tally dips back below the quota.
How’s This Limit Calculated?
Your tenant’s TERRL isn’t just a random number pulled out of a hat—it’s tied to how many email licenses you’ve got. Microsoft’s got a fancy formula for it:
500 × (Purchased Email Licenses^0.7) + 9,500
Let’s break that down with a couple of examples:
- Got 1 license? Your daily limit is 10,000 external recipients.
- Running 100 licenses? You’re looking at about 22,059 external recipients.
- Big player with 10,000 licenses? You can hit up to 324,979 external recipients a day.
The more licenses you have, the higher your cap—so it scales with your organization’s size. But here’s the kicker: this is a 24-hour sliding window, not a midnight reset. Think of it like a rolling tally that constantly checks the last 24 hours of activity. If you max out, you’ll need to wait for some of those earlier sends to “age out” before sending more.
What Happens If You Hit the Limit?
Go over your TERRL quota, and Exchange Online will throw up a roadblock. Any additional emails to external recipients get blocked, and senders will see a non-delivery receipt (NDR) explaining why. Don’t worry, though—internal emails within your tenant aren’t affected, so your team can keep chattering away. Once your 24-hour external recipient count drops below the limit, you’re back in business.
- Trial tenants: 550 5.7.232 - Your message can't be sent because your trial tenant has exceeded its daily limit for sending email to external recipients (tenant external recipient rate limit)
- Non-trial tenants: 550 5.7.233 - Your message can't be sent because your tenant exceeded its daily limit for sending email to external recipients (tenant external recipient rate limit)
Tracking It All with a Shiny New Report
Microsoft’s not leaving you in the dark. They’re tossing in a handy new tool to help you keep tabs on this limit. Head over to the Exchange Admin Center (EAC), pop into Reports > Mail Flow, and look for the Tenant Outbound External Recipients Rate report. It’s your one-stop shop for:
- How many external recipients you’ve emailed.
- Your tenant’s daily TERRL quota.
- What chunk of that quota you’ve used up.
- How many recipients got blocked (if you crossed the line).
Plus, it’ll tell you whether TERRL enforcement is switched on or off for your tenant. For example, if you’ve got over 500 licenses, you’ll see “Disabled” until March 31, 2025—that’s when Microsoft flips the switch for larger tenants. Smaller setups (25 licenses or fewer) start seeing enforcement as early as April 3, 2025, with a phased rollout wrapping up by April.
Why This Matters to You
If your organization sends a ton of external emails—like newsletters, customer updates, or logistics notifications—this could shake things up. Microsoft’s telemetry suggests most tenants won’t notice a blip, but it’s worth a quick check. Are you close to your TERRL cap? Do you rely on third-party services (like email signature tools) that might double-count messages? Now’s the time to audit your email habits.
For those who do need to blast out high volumes, Microsoft’s nudging you toward alternatives like Azure Communication Services. It’s their pay-as-you-go solution built for bulk emailing, leaving Exchange Online free for everyday chatter.
Get Ahead of the Game
TERRL’s coming whether we like it or not, so why not get proactive? Fire up that new EAC report when it drops and see where you stand. If you’re pushing the limits, start planning now—whether that’s tweaking workflows or exploring other emailing options. Microsoft’s giving us a heads-up to adapt, and with a little prep, you’ll keep your email engine humming.
Below is the timeline provided by Microsoft
| Phase | Enable enforcement for tenant group | Rollout start date |
| 1 | Tenants with <= 25 email licenses | April 3, 2025 |
| 2 | + additional tenants with <= 200 licenses | April 10, 2025 |
| 3 | + additional tenants with <= 500 licenses | April 17, 2025 |
| 4 | + all remaining tenants | May 1, 2025 |
What do you think—will TERRL cramp your style, or is it a non-issue for your team?
