[Exchange Web Services] Sending email failed due to the following error: Unsupported restriction type

Getting this error after sending large email with 110mb pdf attachement. The mail is correct sended and received.

[Exchange Web Services] Sending email failed due to the following error: Unsupported restriction type.

test configuration:
emclient [8.0.2891.0] free
Kerio Connect 9.2.12 Patch 1

There is no way to stop / end this error. Account is completely damaged, is not receieving any mails. Only option to fix the error is by removing the mailaccount, and reconfigure it.

In the logging section:
|11-7-2020 18:44:57|xx@xx.xx Exchange Web Services Sending email||—|---|
|11-7-2020 18:44:57|xx@xx.xx Exchange Web Services Sending email: {filename of document.pdf}|
|11-7-2020 18:45:06|xx@xx.xx [Exchange Web Services] MailClient.Storage.Application.OperationException: Sending email failed due to the following error: Unsupported restriction type.|
|11-7-2020 18:45:06| —> Microsoft.Exchange.WebServices.Data.ServiceResponseException: Unsupported restriction type.|
|11-7-2020 18:45:06| at Microsoft.Exchange.WebServices.Data.ServiceResponse.InternalThrowIfNecessary()|
|11-7-2020 18:45:06| at Microsoft.Exchange.WebServices.Data.ServiceResponse.ThrowIfNecessary()|
|11-7-2020 18:45:06| at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest1.Execute()| |11-7-2020 18:45:06| at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems[TItem](IEnumerable1 parentFolderIds, SearchFilter searchFilter, String queryString, ViewBase view, Grouping groupBy, ServiceErrorHandling errorHandlingMode)|
|11-7-2020 18:45:06| at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems(FolderId parentFolderId, SearchFilter searchFilter, ViewBase view)|
|11-7-2020 18:45:06| at MailClient.Protocols.Exchange.ExchangeMailSynchronizer.<>c__DisplayClass25_0.b__0(WorkerStatus status, CancellationToken cancellationToken)|
|11-7-2020 18:45:06| at MailClient.Protocols.Exchange.ExchangeGenericCommand.Execute(WorkerStatus status)|
|11-7-2020 18:45:06| — End of inner exception stack trace —|
|11-7-2020 18:45:06| at MailClient.Protocols.Exchange.ExchangeGenericCommand.Execute(WorkerStatus status)|
|11-7-2020 18:45:06| at MailClient.Commands.Command.Process(WorkerStatus status)|
|11-7-2020 18:45:06|System.Threading.Tasks.TaskCanceledException: A task was canceled.|
|11-7-2020 18:45:06| at MailClient.Storage.Synchronization.FolderSynchronizerExtensions.SynchronizeSubfoldersAsync(IFolderSynchronizer synchronizer, Folder folder, SynchronizationPriority priority, CancellationToken cancellationToken)|
|11-7-2020 18:45:06| at MailClient.Protocols.Exchange.ExchangeAccount.SynchronizeIntAsync(Boolean forced)|
|11-7-2020 18:45:06| at MailClient.Protocols.Common.SynchronizableMailAccount.<>c__DisplayClass6_0.<b__0>d.MoveNext()|