Outlook for Mac reaches 46.76 GB — EWS GetStreamingEvents retry loop and retained network tasks after sleep/VPN interruption

Question

Outlook for Mac reaches 46.76 GB — EWS GetStreamingEvents retry loop and retained network tasks after sleep/VPN interruption

Akim Shepovalov 0

CleanShot 2026-10-06 at 11.37.58@2x

Is anyone else experiencing extreme memory growth in Outlook for Mac when using an on-premises Exchange account over a corporate VPN, particularly after sleep/wake or a temporary loss of connectivity?

On October 6, 2026, after leaving Outlook running overnight, Activity Monitor showed 46.76 GB for Microsoft Outlook on a Mac with 64 GB RAM. System-wide compressed memory was 31.30 GB, swap usage was 2.53 GB, and memory pressure was yellow. Outlook 16.112.1 was installed when this was checked.

This has been recurring for months. A new Mac, a newly created Outlook profile, reinstalling Outlook, and switching between versions 16.111.3 and 16.112.1 did not resolve it.

Environment:

Outlook for Mac, versions 16.111.3 and 16.112.1 affected.

One work account on Exchange Server on-premises, accessed using EWS.

Exchange is reachable only through a corporate VPN.

Earlier detailed reproduction and diagnostics were collected on macOS 26.6.2.

Version 16.113.3 has not yet been confirmed either affected or fixed in my testing.

Earlier diagnostic findings:

After sleep/wake and a temporary loss of access to Exchange, Outlook resumed using an existing EWS SubscriptionId without creating a new streaming subscription.

GetStreamingEvents then repeated approximately 10–11 times per second.

The responses were recorded as HTTP 200 with Size 0, typically completing in about 70–100 ms.

Memory continued growing, approximately 2.6 GB per hour in one measured interval.

Heap inspection found large numbers of retained __NSCFLocalDataTask objects and associated networking objects.

In one controlled interval, CFNetwork recorded 1,307 successfully completed tasks, while 1,307 corresponding task objects remained alive in the heap.

Allocation tracing attributed 1,000 of 1,003 sampled task allocations to a recurring HxCore → NSURLSession creation stack.

A separate manual EWS test using a newly created streaming subscription and appropriate affinity information stayed open for over 90 seconds and returned NoError / ConnectionStatus=OK. This suggests that the endpoint can support normal streaming, although the exact cause of Outlook's empty responses still needs investigation.

These findings suggest a combination of an EWS subscription recovery/retry problem and retention of completed network tasks. The October 6 memory spike has not yet had the same heap-level analysis.

If you have a similar problem, please reply with:

Your Outlook and macOS versions.

Account type: Exchange on-premises, Microsoft 365, IMAP, etc.

Whether a VPN is required.

Whether growth starts after sleep/wake or a network interruption.

Approximate starting and peak memory usage.

Whether Outlook 16.113.3 or a later version changes the behavior.

Please do not post credentials, server addresses, subscription IDs, or unredacted logs.

Could a Microsoft representative confirm whether this EWS/HxCore behavior is a known issue and provide a bug reference, a supported workaround, or a version containing a fix? I would appreciate escalation beyond profile recreation, since a fresh profile and another Mac did not resolve the issue.

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1 answer

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Answer 1

Dear @Akim Shepovalov,

I hope you’re having a good day.

Thank you for the extremely detailed investigation and for sharing the diagnostics.

Based on what you've described, I have not found any publicly documented Outlook for Mac issue that specifically matches this combination of:

Exchange Server on-premises accessed via EWS
VPN-only connectivity
Memory growth after sleep/wake or network interruption
Repeated GetStreamingEvents activity with empty responses
Retained networking objects and sustained memory growth

What stands out is that you've already ruled out many of the usual suspects by testing on a different Mac, creating a new profile, reinstalling Outlook, and reproducing the behavior across multiple Outlook versions. That makes this look less like a profile corruption issue and more like a client-side Outlook behavior that may require engineering investigation.

At this point, I would recommend opening a Microsoft support case and providing a summary of the diagnostics you've already collected. The details regarding EWS streaming recovery, task retention, heap analysis, and reproducibility after VPN interruptions are far more valuable than the standard profile recreation workflow and should help Support understand why the issue warrants deeper investigation.

You can raise support ticket from Microsoft 365 Admin Center>Support>Help & Support.

For reference:  Get support | Microsoft Docs  

User's image

If you're an end user, I'd recommend working with your Microsoft 365 administrator or IT team and asking them to raise the case on your behalf. If they can open a support request, be sure to reference that the issue reproduces on multiple Macs and persists after creating a new Outlook profile and reinstalling Outlook.

One additional data point that may help narrow things down is whether you've had a chance to reproduce the issue on Outlook 16.113.3 or later. Since your previous testing focused on 16.111.3 and 16.112.1, confirming the behavior on a newer build could help determine whether the issue is still active or may already have been addressed.

Thank you again for sharing such a thorough analysis. This is one of the most detailed Outlook for Mac investigations I've seen in the community, and I hope Microsoft Support can use the information you've gathered to pursue the issue further.

Warm regards,

If the answer is helpful, please select "Yes, accept answer". If you have any questions or new updates, please feel free to comment below.

Akim Shepovalov 0 Reputation points

2026-10-06T10:21:01.85+00:00

Update: I have now installed Outlook for Mac version 16.113.3 (26092714), and the memory growth problem persists. Updating to this version has not resolved it.

Unfortunately, I cannot open a formal support ticket. I am based in Russia and, given the current purchasing restrictions, I do not have a licensed installation that provides access to Microsoft support. I mention this to explain why I cannot follow the suggested support route; I am not asking for an exception to licensing or support eligibility requirements.

My purpose in posting here is simply to help other users experiencing the same problem and make the diagnostic findings available to Microsoft and the community. I am not seeking any compensation or personal benefit.

If other users can reproduce this behavior, please share your Outlook version and relevant details here. If a moderator or Microsoft representative can pass this report to the Outlook for Mac engineering team, I would appreciate it. I understand that a public forum report does not replace a formal support case, but I hope the evidence can still contribute to identifying and fixing the issue.
Liora 2,090 Reputation points Independent Advisor

2026-10-06T16:02:55.4766667+00:00

Hi @Akim Shepovalov,

Thank you for the update, and thank you as well for the thoughtful and professional way you've approached this investigation.

I appreciate you sharing the additional finding that Outlook 16.113.3 (26092714) continues to exhibit the same behavior. That helps narrow things down and suggests this is not something that was addressed between the versions you've tested.

I also appreciate your clarification regarding support access. Given the circumstances you've described, I completely understand why opening a formal support case is not a viable option for you at this time.

Perhaps most importantly, thank you for taking the time to document your findings so thoroughly and share them with the community. The level of detail you've provided regarding EWS behavior, network task retention, memory growth patterns, and reproducibility after VPN interruptions is valuable. Even if this thread does not result in an immediate fix, it creates a useful reference point for others who may encounter the same issue in the future.

If you feel my response has been helpful, you might consider marking it as the answer. Doing so can make the thread easier to find for other users experiencing similar Outlook for Mac memory growth issues and looking for information about potential causes, troubleshooting already performed, and current findings.

Thank you again for your contribution to the community and for sharing your investigation in such a constructive manner.

Kind regards.