eM Client 11.0.1201.0 (MSIX) breaks iCalendar handling in Microsoft Outlook 2010

[Achma]

Environment

• Windows 11 Pro, build 10.0.22631
• eM Client 11.0.1201.0 x64, installed as a packaged app (eMClient.20054CA46072C_11.0.1201.0_x64__veq4nz3ze5v72); reproduced with 11.0.1267.0 as well (see below)
• Microsoft Outlook 2010 32-bit (14.0.7268.5000), installed side by side
• Installed via winget install --id eMClient.eMClient -e. This installs only the MSI “eM Client (Updater)” (C:\Program Files (x86)\eM Client\MailClient.exe), which downloads and installs the MSIX package when eM Client is started.

Problem

After installing eM Client, Outlook can no longer open or export .ics files. Opening an .ics file first showed “Either there is no default mail client or the current mail client cannot fulfill the messaging request” (while eM Client was the default MAPI client). After setting Outlook as the default mail client, the error became “The file … is not a valid Internet Calendar file”. This happened even with minimal, well-formed .ics files. Exporting one of Outlook’s own appointments with AppointmentItem.SaveAs(path, olICal) also failed (“The operation failed”).

Findings

• A Process Monitor trace of the failing export shows that Outlook reads HKCU\Software\Clients\Mail and HKLM\SOFTWARE\Clients\Mail and then opens HKLM\SOFTWARE\Clients\Mail\PackagedMail\eMClient.20054CA46072C_11.0.1201.0_x64__veq4nz3ze5v72, including its ClsidExtended value, immediately before the operation fails. It never touches the target file.
• With that registry key removed, the error changed to “Cannot find this file”, so the failing step depends on the packaged registration.
• After uninstalling the eM Client package and restarting Outlook, .ics export and import work normally again.
• Reproduced: after the package had been removed and Outlook worked again, I started MailClient.exe from the updater. It reinstalled the MSIX package, this time as 11.0.1267.0. After restarting Outlook, the iCalendar export failed again (“The operation failed”), and HKLM\SOFTWARE\Clients\Mail had been reset to PackagedMail by the installation (it was Microsoft Outlook before; HKCU stayed Microsoft Outlook). After removing the package, resetting the HKLM value and restarting Outlook, the export worked again.
• The behaviour is therefore not limited to an upgrade from an older version: a fresh install via winget leads to the packaged variant and to the same failure.
• Outlook has to be restarted after installing or removing the package, because it appears to read the list of registered mail clients at startup.

Relation to the known “default email program” message

This is related to, but goes beyond, the thread “Error on Windows 11 with eM Client v11: Microsoft Outlook (Classic) is not running as the default email program” (Error on Windows 11 with eM Client v11 Microsoft Outlook (Classic) is not running as the default email program). There, the message is attributed to Outlook and the advice is to set Outlook as the default mail client. In my case, setting Outlook as the default (HKCU and HKLM) removed only the first message. Outlook’s iCalendar handling stayed broken until the packaged eM Client was uninstalled, so this is not just a question of the default mail client setting.

Request

Please check why the MAPI registration of the packaged eM Client (PackagedMail, ClsidSimple/ClsidExtended) interferes with Outlook, and whether a non-packaged installer avoids the problem.

[jr_gn]

eM Client 11 Beta: three MAPI/MMGA error dialogs after MSI-to-MSIX upgrade

Same issue here after the automatic upgrade from eM Client 10.4 (MSI) to 11.0.1201 (MSIX) on Windows 11 Pro 26H2, with classic Outlook (Microsoft 365, 64-bit). Since the upgrade, every Outlook add-in that uses Extended MAPI through the Windows MAPI stub (mapi32.dll) fails with 0x80004002 (E_NOINTERFACE). In my case TechHit SimplyFile no longer loads any folders and TechHit AccountCheck logs the same error. Outlook itself keeps working. What I found: The MSIX package registers itself as a pac…

Related issues.

Following.

[SimonVandenhoudt]

Additional findings: Windows 10, live crash dump and taskbar behaviour

I can confirm a very similar issue on Windows 10, not just Windows 11.

Environment

• Windows 10 Pro 22H2, build 19045
• Microsoft Outlook 2010 32-bit, version 14.0.7268.5000
• eM Client 11.0.1201.0 x64
• The actual eM Client executable is installed under C:\Program Files\WindowsApps\eMClient.20054CA46072C_11.0.1201.0_x64__veq4nz3ze5v72, confirming that the running application is the MSIX package, despite having the eM Client Updater listed separately.

Reproduction and additional symptoms

• Opening an ICS file with Outlook closed starts Outlook, which shows a blank/grey calendar window with a spinning cursor, displays the default-mail-client warning twice, and then crashes.
• Opening an ICS file while Outlook is already running produces the two warnings followed by “The file is not a valid Internet Calendar file”; Outlook stays open.
• Exporting a test appointment from Outlook to ICS also crashes.
• The issue persists in Outlook Safe Mode and with a new, empty Outlook profile. A minimal ICS file reproduces the problem too.
• Outlook’s built-in repair and Windows component repair (DISM and sfc /scannow) did not resolve it.

Live debugger findings

I reproduced the crash under WinDbg. The exception is:

0xc0000005 — Access violation

The faulting function is:

mmgaclient!PersistedMmgaSessions::ReleaseSession+0x91

The instruction attempts to read [eax-4] with eax=00000000. The stack shows a background thread in mmgaclient.dll. The loaded DLL is:

C:\Windows\SysWOW64\mmgaclient.dll

Version 10.0.19041.4355.

This is the same function and exception pattern as in my earlier crash dump. During startup, MAPI32 also logs:

80073D54 — The process has no package identity.

PackagedMail registration

My registry contains:

HKLM\SOFTWARE\Clients\Mail\PackagedMail\eMClient.20054CA46072C_11.0.1201.0_x64__veq4nz3ze5v72

with these values:

• ClsidSimple = {740C833D-BD87-9A6B-73D4-C076D26AACD7}
• ClsidExtended = {B312B36E-6D5E-776B-C629-5EFD1A3E03CF}

The default value of HKLM\SOFTWARE\Clients\Mail is still Microsoft Outlook on my system, so the problem persists even with Outlook registered as the machine-level default mail client.

Taskbar and process behaviour

When the Outlook warning appears, its taskbar button is grouped immediately to the right of the eM Client button. Moving the eM Client button with 7+ Taskbar Tweaker moves the warning’s button with it. If eM Client is closed, the warning appears as a new, separate item at the end of the taskbar.

I also found five instances of MmgaServer.exe still running after closing both Outlook and eM Client. The executable is located in C:\Windows\System32; its file version is 10.0.19041.4355, and its company metadata says Microsoft.

These observations do not prove that the taskbar grouping or the MmgaServer.exe processes cause the crash, but they may help explain the connection between the packaged eM Client registration, Windows MAPI/MMGA and Outlook’s iCalendar handling.

Question: Could the MSIX PackagedMail registration, particularly ClsidExtended, cause Outlook 2010’s iCalendar handling to fail on Windows 10 as well? Is there a supported way to prevent this conflict while keeping eM Client 11 installed and usable, rather than uninstalling the package and having the issue return after reinstalling it?

[RKCole]

I ran the registry patch you provided but still have the same pop from Microsoft Outlook regarding no default mail client