Did you ever try to reset the ActiveSync device cache? Login to your mailcow UI with your affected mailbox account, you can find it in the Settings tab

I reseted the cache and tested it on Laptop and Desktop. Didnt work.

Then I’m out of ideas… the last thing you can try is enable debug logging in Sogo for ActiveSync and check if there is an error message regarding a calendar object which breaks the sync…

Is this a error?

mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 syslog-ng[9]: Error processing log message: </Ping>
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [67]: <0x0x5626af8e3e60[SOGoWebDAVAclManager]> entry '{DAV:}write' already exists in DAV permissions table
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [67]: <0x0x5626af8e3e60[SOGoWebDAVAclManager]> entry '{DAV:}write-properties' already exists in DAV permissions table
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [67]: <0x0x5626af8e3e60[SOGoWebDAVAclManager]> entry '{DAV:}write-content' already exists in DAV permissions table
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [68]: <0x0x5626af7caa00[SOGoWebDAVAclManager]> entry '{DAV:}write' already exists in DAV permissions table
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [68]: <0x0x5626af7caa00[SOGoWebDAVAclManager]> entry '{DAV:}write-properties' already exists in DAV permissions table
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [68]: <0x0x5626af7caa00[SOGoWebDAVAclManager]> entry '{DAV:}write-content' already exists in DAV permissions table
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [68]: <0x0x5626af487c20[SOGoActiveSyncDispatcher]> Sleeping 45 seconds while detecting changes for user stefan@xxx.xxx in Ping...
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:24 b473c284a156 sogod [67]: <0x0x5626af4884d0[SOGoActiveSyncDispatcher]> Sleeping 45 seconds while detecting changes for user ordination@xxx.xxx in Ping...
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:25 b473c284a156 sogod [63]: |SOGo| starting method 'POST' on uri '/SOGo/Microsoft-Server-ActiveSync?Cmd=Ping&User=hans@xxx.xxx&DeviceId=1D646C8CC0DD41968DC8A7D7C5DFC92D&DeviceType=WindowsOutlook15'
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:25 b473c284a156 sogod [63]: <0x0x5626af14b230[SOGoCache]> Cache cleanup interval set every 900.000000 seconds
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:25 b473c284a156 sogod [63]: <0x0x5626af14b230[SOGoCache]> Using host(s) 'memcached' as server(s)
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:25 b473c284a156 sogod [63]: <0x0x5626af5ac9e0[SOGoActiveSyncDispatcher]> EAS - request for device 1D646C8CC0DD41968DC8A7D7C5DFC92D: <?xml version="1.0"?>
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:25 b473c284a156 syslog-ng[9]: Error processing log message: <!DOCTYPE ActiveSync PUBLIC "-//MICROSOFT//DTD ActiveSync//EN" "http://www.microsoft.com/">
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:25 b473c284a156 syslog-ng[9]: Error processing log message: <Ping xmlns="Ping:">
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:22:25 b473c284a156 <HeartbeatInterval>3540</HeartbeatInterval>

or this:

mailcowdockerized-sogo-mailcow-1 | Sep 28 11:46:38 eb0d501e5a4a syslog-ng[7]: Error processing log message: </Sync>
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:46:38 eb0d501e5a4a sogod [57]: |SOGo| request took 0.911131 seconds to execute
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:46:38 eb0d501e5a4a sogod [57]: 84.112.35.208 "POST /SOGo/Microsoft-Server-ActiveSync?Cmd=Sync&User=hans@xxx.xxx&DeviceId=1D646C8CC0DD41968DC8A7D7C5DFC92D&DeviceType=WindowsOutlook15 HTTP/1.0" 200 0/12331 0.913 - - 0 - 13
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:46:43 eb0d501e5a4a sogod [57]: |SOGo| starting method 'POST' on uri '/SOGo/Microsoft-Server-ActiveSync?Cmd=Sync&User=hans@xxx.xxx&DeviceId=1D646C8CC0DD41968DC8A7D7C5DFC92D&DeviceType=WindowsOutlook15'
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:46:43 eb0d501e5a4a sogod [57]: <0x0x56082e66a9c0[SOGoActiveSyncDispatcher]> EAS - request for device 1D646C8CC0DD41968DC8A7D7C5DFC92D: <?xml version="1.0"?>
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:46:43 eb0d501e5a4a syslog-ng[7]: Error processing log message: <!DOCTYPE ActiveSync PUBLIC "-//MICROSOFT//DTD ActiveSync//EN" "http://www.microsoft.com/">
mailcowdockerized-sogo-mailcow-1 | Sep 28 11:46:43 eb0d501e5a4a syslog-ng[7]: Error processing log message: <Sync xmlns="AirSync:">

Nope - i checked. Everything is set to Berlin. Mailcow config, Sogo Settings and Linux Server

17 days later

The issue is due to an arithmetic overfow within outlook while sending the “new” event as mentioned in this comment of this bug ticket bugs.sogo.nu Icon 0005921: Oulook 2021 (365) stoped syncing via EAS with latest SoGo - SOGo | BTS

bugs.sogo.nu Icon bugs.sogo.nu
0005921: Oulook 2021 (365) stoped syncing via EAS with latest SoGo - SOGo | BTS
AndreyEversebastienqhivert

It is very annoying for us as well. Please vote for the issue to raise awareness on Microsoft side on the following two sites:

I think you are right! I upvoted it.

14 days later

Wohooo! It seems to be solved with the 2410 Update!

Hey @sut,
what Office Version exactly do you have? I just updated to the latest release

learn.microsoft.com
Update history for Microsoft 365 Apps (listed by date) - Office release notes
Provides IT Pros with a complete list of Microsoft 365 Apps releases, organized by date, with links to release notes.
Microsoft Learn
after your post but with my Office Professional Plus 2019 Version 2410 (Build 18129.20116) it ist stilll not working. Also still not working for a friend of mine with Office 365 and the same build.

Edit: Also what version of mailcow are you running? I’ve got version 2024-08a

Sorry - i am dumb…
I tested with the wrong account. I have one account with Caldav Synchronizer and one with eas. Eas still doesnt work.

Sorry for giving false hope.

Microsoft® Outlook® für Microsoft 365 MSO (Version 2410 Build 16.0.18129.20100) 64 Bit

Did you ever try the 32 Bit version? Works flawlessly for me

FYI, I just upgraded to

Microsoft® Outlook® für Microsoft 365 MSO (Version 2410 Build 16.0.18129.20100) 32 Bit

and tested the calendar sync both ways, works like a charm for me. But as I said, it’s the 32Bit version, I think we had this problem once in another thread which also used the 64Bit version

Thanks for the info @DocFraggle! It makes sense that it may only affect the 64bit version since the exception thrown is an arithmetic overflow. Could be a difference here with 64bit and 32bit version.

    Undecided9954 It makes sense that it may only affect the 64bit version since the exception thrown is an arithmetic overflow

    Yes, that could be possible. So give it a try then with the 32Bit version, waiting for an update 🙂

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