v15.5 @ Debian: Exchange Sync results in http 413 error

[Lev]

- v.15.5 @ Debian
- Exchange 2013 (on premise)
- only "standard authentication" is enabled on the EWS site
- client ssl certificates are set to be ignored

The logs will give me this error:

2017/07/20 14:02:39.721|810|0045|Info|Synchronization of GAL started...
2017/07/20 14:02:39.721|810|0045|Info|Synchronization of public folders started...
2017/07/20 14:02:39.722|810|0045|Info|Synchronization of Public Folder Kontakte\NMS Kunden started...
2017/07/20 14:02:40.021|810|0033|Erro|Error while checking contacts from Public Folder Kontakte\NMS Kunden
2017/07/20 14:02:40.026|810|0033|Excpt|Microsoft.Exchange.WebServices.Data.ServiceRequestException: The request failed. The remote server returned an error: (413) Request Entity Too Large. ---> System.Net.WebException: The remote server returned an error: (413) Request Entity Too Large.
at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean requiresSynchronization)
--- End of stack trace from previous location where exception was thrown ---

I tried adjusting the uploadreadaheadsize to different values (even tried the hightes possible state), but i keep getting the same error.

Any ideas?

 

[Lev]

Last night, i did a last attempt on changing the uploadreadaheadsize. This time the value was set to 1048576
Right after the change, it would still not sync.

This morning i figured out, that 3CX had actually synced again.
I cannot tell, what the reason is. Maybe it was just some kind of exchange or IIS cache thing?