I've been having very intermittent issues with Outlook and have not been able to find a solution. Being so intermittent, it's difficult to troubleshoot since it goes up and down frequently on its own, I can't determine if any changes make a difference. Problem occurring on multiple computers and multiple AD accounts / mailboxes but NOT all of them, some work fine.

Outlook "Trying to connect" or "Disconnected" | Send/Receive Error: 0x80040115

I found and tried some generic suggestions that made no difference:

  • ipconfig /flushdns
  • recreating the profile
  • disabling all addins

Problems will last a few minutes or hours then everything works fine for a bit before it returns to the same problem a few minutes or hours later. While it's unable to connect, OWA works just fine, so it's not a server down or ISP problem on either side.

I found some similar reports but Office 365 related so those solutions do not apply to my on-site Exchange 2016.

Error sometimes appears only when sending, other times when receiving.

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Log requested below: https://drive.google.com/file/d/1u6Caav_ukzq9cK5ju_IHBHG8RMYXxQzY/view?usp=sharing

Screenshots: https://drive.google.com/drive/folders/1pd7qO1hVkQXz_axeNlX8WKoRhLuIlHy0?usp=sharing

  • What do the event logs on the Exchange server show? – joeqwerty May 5 at 16:57
  • Do you monitor your router configuration ? to see if a bottleneck affect your network. – yagmoth555 May 5 at 17:17

1 Where did you encounter this issue? Internal client, external one or both of them?

2 Make sure update your office 365 and windows to the latest version.

3 Try configuring these problematic mailboxes on other clients which work well, and see if the issue still exists. If the issue only happened on specific clients, the reasons to cause it could be some problems of the clients themselves. Check if the following guidance to fix the 0x80040115 error is helpful: FIX: Microsoft Outlook error 0x80040115

4 Try running the following commands in EMS to see the configurations of your Exchange server, and you could attach the log0.txt file to your edited post(Please alter any sensitive names such as server FQDN/URLs.):

Get-CASMailbox -Identity <Problematic Mailbox Identity> | ft Name, MapiHttpEnabled -AutoSize

Start-Transcript log0.txt
Get-OabVirtualDirectory | fl server, Name, *URL*, *auth*
Get-WebServicesVirtualDirectory | fl server, Name, *URL*, *auth*
Get-EcpVirtualDirectory | fl server, Name, *URL*, *auth*
Get-OwaVirtualDirectory | fl server, Name, *URL*, *auth*
Get-ActiveSyncVirtualDirectory | fl server, Name, *URL*, *auth*
Get-ClientAccessServer | fl Name, OutlookAnywhereEnabled, AutodiscoverServiceInternalUri
Get-ExchangeCertificate | fl FriendlyName, Subject, CertificateDomains, Services, Issuer, *not*, Status
Get-OutlookAnywhere | fl server, Name, *URL*, *hostname*, *auth*
Get-MapiVirtualDirectory | fl server, Name, *URL*, *auth*
Get-OrganizationConfig | fl *mapi*
Get-ClientAccessArray | fl
Get-ExchangeServer | fl *version*
get-service *Exchange* | ft -AutoSize

5 Check if there was an error event in the Event Viewer after failing to build connections.

  • 1. Both internal and external | 2. Various versions of Outlook are behaving the same, including Office 365 and retail 2016 | 3A. I have not tried this yet but will soon | 3B. This link/article has very generic suggestions that I've tried a dozen times. Especially generic is flushdns that never does a thing as I wouldn't expect it to since it almost seems unrelated. | 4. Log linked | 5. Nothing in event log after the error in Outlook – prl77 May 6 at 20:32
  • @prl77 What's the result if you run the cmdlet Get-CASMailbox -Identity <Problematic Mailbox Identity> | ft Name, MapiHttpEnabled -AutoSize? According to your attached log, the configurations which are different from mine are the ExternalClientAuthenticationMethod and InternalClientAuthenticationMethod, check if the NTLM authentication is disabled on these problematic clients or there is a group policy to disable it. – Ivan_Wang May 7 at 7:20
  • Result of this cmdlet is empty MapiHttpEnabled column for all accounts, problematic and not. I turned on NTLM auth based on this: support.robinpowered.com/hc/en-us/articles/… – prl77 May 7 at 16:12
  • Because the MapiHttpEnabled settings for mailboxes are $null, the mailboxes use the organization setting(MapiHttpEnable: True) for MAPI over HTTP(Get-OrganizationConfig | fl MapiHttpEnabled), more details about the MapiHttpEnabled(docs.microsoft.com/en-us/powershell/module/exchange/…). Therefore, the connection between clients and server is built by Mapi over Http, and you could check that by the Connection Status function in Outlook(Protocol field). What's the status in Connection Status when happening the connection issue? – Ivan_Wang May 10 at 10:09
  • After disabling MAPIHTTP I got no connection at all, despite Status showing "established" - see screenshot error6. Screenshot error5 shows how it looks when things are fine but a few minutes later I get screenshot error5 when it does not work. Link to screenshots in original post. – prl77 May 10 at 19:54

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