Update 7/14/2025: Updated the FAQ.
As with all cloud services, Exchange Online imposes service limits to prevent misuse of Exchange Online resources and ensure availability for all users. For examp...
Updated Jul 14, 2025
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Nice...
Why does it take into account mails sent from an on-premise server, not relayed through our Office 365 tenant ?
We now have our email system blocked all day round, thank you Microsoft.
Arindam_Thokder
Microsoft
MicrosoftBenoitGu -
TERRL does NOT take into account mails sent from an on-premises server, not relayed through our Office 365. If your question is related to email which are sent from On-premises directly to internet that is never routed through sender's Exchange online tenant, they are not counted against the TERRL limit.
However, we have seen cases where email sent from on-premises gateway is wrongly attributed to their own tenant before sending it to recipient's tenant. You might have the same issue. This happens because of the misconfiguration where certificate used by the on-premises server or gateway matches the inbound connector of sender's tenant. I explained about this in the video here- Establishing Exchange Hybrid Mailflow (watch full or start from 16:30)
Arindam_Thokder No, it is definitely not that.
The mails are sent from an on-premises server, not linked to our O365 tenant in any way, except that it sends emails on the same domain name.
So there is no reason O365 should count the mails sent from that server against our TERRL, except it does. Not all mails, of course (that would not be possible), but any mail sent from that server to another O365 customer, is taken into account.- Arindam_Thokder
Try to track the email send from On-premises to Internal on your tenant. This will give some idea if it is going through the tenant. If the email is not sent through the tenant, there is no way TERRL can calculate that, it is technically not possible.
I did track the mails, they were NOT going through our tenant. More explanations in my response to Kenneth below.
BenoitGu that is concerning to read. Could you provide some evidence to that?
We have some customers that sometimes send high volumes of mails from their on premise systems and we can easily route that mail directly outbound over a public IP and thus not burden their ExO tenant with these mails since it will not pass there.
This would mean, depending on where the mails gets delivered, some of it would count against their TERRL.
However, I would expect that this is not intended and a bug which should get fixed?Kenneth650 , so we managed to solve our problem, somehow.
So, we have an on-premise mail server (not even an Exchange Server) that sends mails from our solution to our clients from the address mailto:email address removed for privacy reasons. Our tenant also uses the domain example.com.
The problem we were experiencing was, any mail sent from the on-premise server to clients who have their mails on Exchange 365 would be counted against our TERRL.
Apparently, there was a connector I was not aware of between our tenant and the on-premise server, that may explain it. It was disabled. At the same time, I contacted the support about this problem, and they told me they were going to fix the problem.
I don't know which of these two actions actually solved it (disabling the connector or the support actions), but ~3 hours later, everything was back to normal, and no problems since.
