When performing day-to-day email tasks, it is very unlikely that you hit one of the many Office 365 email limits. However, when moving huge amounts of email data (e.g. when performing an email migration), these limits can cause several problems.
In the following, we’ll explain when best to disable Microsofts limits and show you how you can easily disable Microsofts so-called “EWS throttling” for Office 365 and Exchange Online accounts!
Summary:
Microsoft applies email limits for Office 365 and Exchange Online mailboxes (“ESW throttling”). These limits can cause issues during large email migrations, such as disconnects or incomplete migrations. By disabling throttling temporarily, you can avoid these problems, especially when migrating large mailboxes (10 GB+).
➡️ To disable MS 365 EWS throttling temporarily, simply follow these instructions.
Office 365 Email Limits:
What is EWS Throttling MS 365 / Exchange Online?
Microsoft 365 as well as Exchange Online apply several email limitations to protect the reliability, performance, and scalability of their multi-tenant cloud infrastructure. These limitations are summarised under the term “EWS throttling”.
While Office 365 email limits usually don’t affect users in their day-to-day work, they can become problematic when moving large amounts of data, e.g. when migrating to Office 365 or performing an email migration from Microsoft to another provider. For email migrations, the following limitations become relevant:
MS 365 Email Limits Relevant for Email Migration:
| Limit | Value |
| Sending / Receiving limit | 3600 msgs per hour |
| Maximum concurrent IMAP connections | 20 per mailbox |
| Download & upload capability | ~20 GB per day (according to our performance tests) |
| Large folder impact | Folders containing > 100,000 items lead to degraded performance or timeouts |
➡️ As a rule of thumb, you can expect MS 365 to throttle your account connection after migrating more than 20 GB of email data / day.
✅ If you need to migrate a large mailbox to or from Office 365, this article explains different migration approaches and offers helpful tips for a smooth migration!
Microsoft EWS Throttling:How Does Microsoft’s Throttling Affect Email Migrations?
When migrating large email accounts, it is possible to exceed one or multiple Office 365 email limits. If this happens, Microsoft closes the IMAP connection to its servers and the migration has to be restarted.
In the following use cases, Office 365 email limits can easily be exceeded:
- migration of large mailboxes (> 10 GB)
- huge amounts of incoming and / or outgoing emails in a short period of time
- many simultaneous connections to the MS 365 mailbox while the migration is in progress
- more than one email migration or backup tool is used simultaneously (as they interfere with each others progress)
✅ MailJerry has built-in mechanisms to respect Microsoft’s limitations.
While the default settings work great for most migrations, there may still be situations that lead to disconnects.
Our Recommendation:When to Disable EWS Throttling
In general, we recommend to temporarily disable EWS throttling when migrating mailboxes large mailboxes (= 10 GB or more) from or to Microsoft 365. Disabling limits helps your migration to run smoothly, reduces migration time and makes your life easier as you won’t have to worry about disconnects.
➡️ If your migration finishes incompletely, please also disable EWS throttling, wait 15 minutes, and perform a new sync (e.g. hit the “Sync Now” button).
Typical error messages caused by Office 365 email limits:
If your migration breaks because Office 365 limits were exceeded, you usually see one or both error messages in your migrations log file:
Trying command when NOT connected!(Usually fired many times.)
Request is throttled. Suggested Backoff Time: 299961 milliseconds(Usually fired once, followed by many “Trying command when NOT connected!” errors.)
You should also consider disabling MS 365 throttling in the following cases:
- your mailbox experiences lots of incoming or outgoing traffic
- the mailbox is used by more than 1 person at the same time (while the email migration is running)
- you’re initialising / using an additional backup tool
➡️ If a backup tool is active for your Microsoft 365 mailbox, please disable the tool (if possible) while the mail migration is running. This prevents the mailbox from having to handle additional load.
Increase Office 365 Email Limits:How to Disable MS 365 EWS Throttling
To disable the MS 365 throttling limits temporarily, follow these steps:
1. Log in to the Microsoft 365 admin center at https://admin.microsoft.com
2. In the left toolbar, expand the Support section and click on Help & support.
(In case you don’t see the support section, click on “Show all”).
3. In the FAQ search box “How can we help”, write Increase EWS Throttling Policy and click on the blue arrow or hit enter.
4. In the search result under “Run diagnostic”, click on Run Tests.
5. Wait until the test finishes. Now you can disable MS 365 EWS throttling by selecting a duration of 30, 60, or 90 days.
6. Enable the checkbox to acknowledge the setting change and click on the Update button
7. Wait until you see the success message (Don’t close the window while the change is being processed!).
⚠️ Important: Now wait at least 15 minutes for the changes to propagate. After that, you can use Office 365 without email throttling limits for the select amount of days.
Microsoft EWS Throttling:Frequent Questions & Answers
Can I disable throttling forever?
Unfortunately, no. The Microsoft throttling cannot be disabled forever, but only for a selected period of 30, 60 or 90 days.
I need to migrate a large / very large mailbox to / from Office 365. Any tips?
Fore sure! This article explains everything you need to know about migrating large amounts of data to or from Microsoft 365 and Exchange Online.
How long does it take until my changes to the throttling limit take effect?
After updating the EWS throttling policy, it usually takes 15 minutes until the update its complete and your changes take effect.
I disabled Microsoft limits, but my migration is still running slowly. Why is that?
Even if disabling Microsofts email limits, Microsoft still limits the data import to 150 MB per every 5 minutes per mailbox.
My Office 365 email migration finished, but there are still messages missing!
If this is the case, please disable MS throttling and perform a new sync but clicking on the “Sync Now” button.
How do I know if throttling limits caused my migration to break?
To find out if your migration broke because of throttling limits or if any other issue caused the error, please open the log file of your migration (go to Overview > Your Migration and click on “Download Log File”). If you see one of the two error messages stated below, your migration was stopped by Microsoft because of exceeded limits:
- Trying command when NOT connected.
- Request is throttled. Suggested Backoff Time: 299961 milliseconds
Where can I learn more about Office 365 / Exchange Online email limits?
To learn more about Office / MS 365 email limits, have a look at the following links:
