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Outlook MAPI connections breaking
Problem reported by Matthew Titley - 10/1/2025 at 5:51 AM
Resolved
Has anyone else seen an uptick in broken MAPI sync connections lately? I've noticed over the past month or so an increase in support calls regarding broken Outlook connections. Customers have reported the classic "Your mailbox has been temporarily moved on Microsoft Exchange server. A temporary mailbox exists..." yadda yadda. As far as I've seen the only fix is to recreate the profile.

What I've been doing is adding the reg key ExcludeExplicitO365Endpoint 1 to the Outlook autodiscover hive, during a remote support session, and then recreating the Outlook profile. It works as a solution but I'm a bit mystified as to why this is happening more frequently lately. It's a fairly quick fix except for the time it takes for the customer's account to fully resync. I haven't upgraded since build 9229 in April. Most users are on either Outlook 2019 or 2021. I suspect it has something to do with Microsoft accounts somehow confusing Outlook but I don't know for sure. Anyway, just curious if this is a localized occurrence or if others have been seeing it also.

Matt
Derek Curtis Replied
10/1/2025 at 6:55 AM
Employee Post
We've not seen an uptick in tickets on this, as far as I know, but I'm curious to know if others are seeing it as well. 
Derek Curtis COO SmarterTools Inc. www.smartertools.com
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Douglas Foster Replied
10/1/2025 at 12:03 PM
I ran into problems four years ago, and solved them by setting two registry keys:
 "ExcludeExplicitO365Endpoint"=dword:00000001
 "ExcludeScpLookup"=dword:00000001

When those are not disabled, it is possible for Office365 to accept the user despite the unauthenticated connection.   Messages sent from the unauthenticated account are accepted and delivered using an SMTP Mail From address of the form  outlook_digitstring@outlook.com, which of course is useless for replies.   That incident happened with a user on a Hosted Exchange domain at a third-party hosting service, not with SmarterMail.   I am guessing that something similar is happening to your damaged users.   
Michael Replied
10/2/2025 at 7:58 AM
We just had a case of this. One user on one domain. Deleted outlook profile and resync.but interesting about the timing. 
Eric Tykwinski Replied
10/2/2025 at 9:04 AM
Matt,

There is a bug just announced about MAPI breaking on Office versions:

I've personally seen this as well this past week with several clients, as well as the temporary mailbox issue and think they may be related.
Michael Replied
10/2/2025 at 2:35 PM
Very interesting. 
Seph Parshall Replied
10/16/2025 at 12:50 AM
Where are those Registry keys located?
I'm having the same problem and it's growing
Eric Tykwinski Replied
10/16/2025 at 7:12 AM
Seph,

Typically, it's this in PowerShell:
Set-ItemProperty -Path “HKCU:\Software\Microsoft\Office\16.0\Outlook\AutoDiscover” -Name ‘ExcludeExplicitO365Endpoint’ -Value 1 -Type DWORD –Force
Version 16.0, might be different, you'll have to look.  ExcludeScpLookup is for a local AD lookup, which you may need, but I usually don't.
Matthew Titley Replied
10/16/2025 at 10:54 AM
@Douglas Foster, I, too, would occasionally have to tackle the issue by using the reg keys but it used to be rare. However, I've noticed this issue becoming far more frequent. Just in the past few weeks I've had a number of support calls where Outlook was losing it's sync status and the only solution (that I've found to work) is to add the ExcludeExplicitO365Endpoint 1 reg key and then recreate the profile.

As I'm sure others have read in IT news, Microsoft is working hard to close the various avenues of Windows access (local or AD) without Microsoft accounts. It's not much of a stretch to believe that Microsoft wants all Outlook accounts to work only through O365. Regardless, this issue will probably become more prevalent to non-O365 hosted email users wanting to use Outlook and MAPI with SmarterMail. It doesn't look like there is anything that ST can do about it, though.

The odd thing is that there is a randomness to it. I can setup a user with Outlook MAPI with no error sometimes. Down the road a few weeks or months it might break. Or, sometimes, I simply cannot create a new Outlook MAPI account without adding the reg key. I'm fairly certain that the common denominator is the user having a Microsoft account address that matches their Smartermail email address.

Matt
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Douglas Foster Replied
10/16/2025 at 1:28 PM
It the O365 option is not forced off, I would worry that Microsoft might create a successful connection with itself in the middle.   Then that connection might or might not work, depending on timing problems and the quality of there implementation.   Of course, it would also be a problem because they would have access to your credentials as well as  your email content.

Several  years ago I tested Outlook Mobile.  The connection worked, but messages were delayed by minutes.
Later, I fought autodiscover performance and reliability problems, and found that the registry changes made the application startup much faster and the connection became reliable.
Matthew Titley Replied
10/21/2025 at 9:50 AM
Two more yesterday, and four more today. Modify reg, create new profile, problem solved, wash, rinse, repeat. The fact that it seems to be happening far more frequently with my hosted customers (based upon the paucity of others reporting the same issue) is worrisome. Guess I'll open a ticket on the issue, but I have my doubts that there is any server configuration or DNS record issue seeing how this has spiked just recently.
Tim Uzzanti Replied
10/21/2025 at 11:35 AM
Employee Post Marked As Resolution
No reason to open a ticket on this.  Nothing we can do; it's just Microsoft boinking Outlook with updates and trying to run things through their servers even though your mail is hosted on different platforms.  Microsoft is not a good actor these days!
Tim Uzzanti CEO SmarterTools Inc. www.smartertools.com
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Mike Mulhern Replied
10/21/2025 at 12:15 PM
Had my first instance of this today.
Matthew Titley Replied
10/21/2025 at 12:36 PM
Hi Tim,

Thanks for the response; it's much appreciated! Seeing how, as a community, we're all in the same boat regarding MAPI and Outlook, it's hard to know what to do other than address the issue ad hoc as customers report problems. That being said, does anyone at ST know exactly what change or update Microsoft has either made or pushed which has resulted in this surge in MAPI problems? The reason I ask is that, for example, if I have one customer with ~40 Outlook 2021/2024 MAPI accounts, to date "only" ~20 have broken and I see no configuration differences among the fleet of devices. 

Is it a specific Windows Update KB patch or something else, such as some change occurring on Microsoft account login? If ST hasn't received any clear information from Microsoft, I would not be surprised in the least, unfortunately. I can only imagine how irritated you must be over this.

Thanks,

Matt
Tim Uzzanti Replied
10/21/2025 at 1:28 PM
Employee Post
We have no idea. We love finding workarounds, but we can’t see anything that would help alleviate the issues. It doesn’t matter whether you’re using SmarterMail, Exchange, or even Office 365; Outlook is truly falling apart at the seams with all the changes Microsoft is making to route more and more traffic through their own servers, whether for autodiscover or actual mail data.

Another issue we’re seeing frequently that is also affecting Office 365 users is:

Almost 50% of our support tickets right now are Outlook-related. It really sucks that we can’t do more to help.

We’ve moved all of SmarterTools off Microsoft products. This comes from someone who built one of the largest Windows hosting companies back in the day — and developed Mail, Stats, and Track products for ISP and hosting companies running Windows.  

We have been using .NET since its inception and during their initial BETA release, we were working very closely with Microsoft on issues.  Now, we just hope they don't boink .NET like they have everything else.  We don’t use Azure or Office365 because they’re kind of awful and getting support is a test of patience, with some incidents going for months. 

Microsoft is a very different company now, and it’s disappointing.
Tim Uzzanti CEO SmarterTools Inc. www.smartertools.com
Oliver Replied
10/21/2025 at 2:08 PM
@Tim, I completely agree with you. Microsoft is just so frustrating!
Seph Parshall Replied
10/21/2025 at 5:23 PM
This issue that Tim links to [on Microsoft website] was my first indicator of a problem. After a while I couldn't re-connect Outlook to the email account on SmarterMail. The only thing that fixed it was the Registry hack. This is only affecting my customers that login to a Microsoft account to activate MS Office. Logging into MS Office in any Office product [Word, Excel, Outlook] for activation should be a red flag for anyone reading this thread. That is the common denominator from my experiences.
Thanks everyone!
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Emory Kempf Replied
10/22/2025 at 9:40 AM
How about you modernize the webmail interface to a point where users can use it as their daily driver? We currently advise users to use webmail as a workaround, but most users find it too cumbersome to use full time. I can provide more details if you are interested improving webmail.

I currently use Spark and enjoy it a lot.


Tim Uzzanti Replied
10/22/2025 at 12:53 PM
Employee Post
We are re-doing Webmail in React (currently Angular).  The new SmarterMail High Availability Hub interface was built on React and is the foundation of the new Webmail moving forward.  It is a major project, Webmail is huge!  We are continuing to improve what we have, building it out, and delivering new features, all while working on the new Webmail simultaneously.  I don’t want to sidetrack this thread discussing more about Webmail and can discuss it more in the future in another thread.  Appreciate the feedback and we will definitely be getting suggestions and guidance from customers as we move forward.   
Tim Uzzanti CEO SmarterTools Inc. www.smartertools.com
I know its a big thing... can tyou replicate the look of outlook in webmail?

Then everybody would be ecstatic :)
Matt Petty Replied
10/23/2025 at 9:13 AM
Employee Post
"How does this look in Outlook/eM Client/Exchange/Google (sometimes)" comes up *often* in our design discussions especially for things like terminology. So hopefully there should already be a lot of cross over in that regard but we overall have a design that we like to stick to across sysadmin <--> users and even at times our other products. From cards, tables, warning messages in card, the color and order of buttons in all the dialogs, etc we try to be very consistent.

For example we did this cross-referencing when we were implementing the delay/schedule message sending, which should be coming down the pipeline very soon.
Matt Petty Senior Software Developer SmarterTools Inc. www.smartertools.com
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