Next time you get the problem can you try to do what is described in bug 3058 instead of a resetfolder:

"... I can make them to show in Outlook by loging into webmail and marking these letters and
right click to theese email and select move to->inbox then Outlook downloads these messages."

===

There are some reports which describing a similar problem with outlook.com
e.g. https://social.technet.microsoft.com/Forums/office/en-US/ecbde6d4-614d-476c-a5f3-490b183b4d66/outlook-2013-missing-email-in-inbox-compared-to-outlookcom?forum=officeitpro

The problem here is the huge amount of data which needs to be analyzed because the it might take some time until the problem occurs.

To analyze were the problem is caused (outlook or sogo) following steps could help:

Enable logging in Outlook 2013:

1. Click File, Options, Advanced
2. Under Other at the bottom click the check box to Enable Troubleshooting Logging
3. Restart Outlook
4. Wait until the problem occurs
5. Disable logging and restart Outlook

The log files are in this directory:

Drive:\Users\accountname\AppData\Local\Temp\EASLogFiles

6. Identify the last mail which is ok in outlook and on server.

   • e.g. https://.../SOGo/so/.../Mail/0/folderINBOX/1261/popupview

7. Identify the email not showing up in outlook but is there on SOGO web.

   • e.g. https://.../SOGo/so/.../Mail/0/folderINBOX/1262/popupview

8. Search Drive:\Users\accountname\AppData\Local\Temp\EASLogFiles\<ID>.xml for e.g.
   <a0_ServerId>1262</a0_ServerId>

9. Check all files to understand what's going on while syncing
   Dir:<ID>.xml* (check the files created before and after the file identified above)
   File: <ID>.sync.1.log

===

Compare the info gathered above with a tcpdump on port 20000:

tcpdump -i lo -s 0 -w /tmp/dump.pcap tcp and port 20000

===

Check sogo.log for any unusual message.

Hello
Can this not also be due to a certificate error as well? On some pc the certificate does not want to take even though I have installed it. After a while it stops syncing and then if you open and close outlook it starts to sync again.

I have also had the stop syncing and will look into the top suggestion maybe I am wrong.

@Sl33py : I'm afraid this is not the same problem you have.
Sync of subfolders works fine, it's just the inbox that stops syncing.
It doesn't help to restart Outlook.
This is on a TS, no certificate problems.
I'll try the logging as described above.

No feedback provided in months, suspending. Make also sure you test the latest stuff before re-opening.