activesync couldn't get server version

Just wanted to try/switch to em Client!
however when connection to our exchange server i get a “couldn’t get server version” error

em Client Version : 7.2.34711.0
Windows 10 1809

Log is as follows :
02:00:04 Online state: changed to online due to NetworkAvailability
02:00:04 claude.nobs@bedag.ch [Exchange Web Services]  MailClient.Accounts.ConnectionException: Couldn’t get server version.
02:00:04    at MailClient.Protocols.Exchange.ExchangeFolderSynchronizer.GetExchangeVersion(WorkerStatus s, CancellationToken c)
02:00:04    at MailClient.Protocols.Exchange.ExchangeGenericCommand.Execute(WorkerStatus status)
02:00:04    at MailClient.Commands.Command.Process(WorkerStatus status)

Exchange Server version unknown, however the same configuration is working in Thunderbird  with ExQuilla. It identifies the server as :
2019-02-27 21:02:08.003 exquilla.native CONFIG Server MajorVersion is 15 MinorVersion is 1
2019-02-27 21:02:08.003 exquilla.native CONFIG Using schema for server version 2010sp1

Is there some way to force this setting in em Client?

attaching the advanced log out :

01:49:16.913|001|   AccountBase.ChangeOnlineState : STATE CHANGE TO online due User
01:49:16.913|019|  
01:49:16.913|019| POST /EWS/Exchange.asmx HTTP/1.1
Content-Type: text/xml; charset=utf-8
Accept: text/xml
User-Agent: eM Client/7.2.34711.0 (ExchangeServicesClient/7.2.34711.0)
Accept-Encoding: gzip,deflate

01:49:16.913|019|
01:49:16.913|019|  
01:49:16.913|019| <?xml version="1.0" encoding="utf-8"?>
01:49:16.913|019| http://www.w3.org/2001/XMLSchema-instance"; xmlns:m=“http://schemas.microsoft.com/exchange/services/2006/messages”; xmlns:t=“http://schemas.microsoft.com/exchange/services/2006/types”; xmlns:soap="" rel=“nofollow” target="" title=“Link httpschemasxmlsoaporgsoapenvelope” type="" value="">http://schemas.xmlsoap.org/soap/envelope/">;
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|

01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019| IdOnly
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|
01:49:16.913|019|

01:49:16.913|019|
01:49:16.913|019|
01:49:16.957|019|  
01:49:16.957|019| HTTP/1.1 503 Service Unavailable
Connection: close
Pragma: no-cache
Content-Length: 62
Cache-Control: no-cache,no-store

01:49:16.957|019|
01:49:16.957|017|   AccountBase.ChangeOnlineState : STATE CHANGE TO offline due BrokenConnection

any idea? I face the same situation and my emails are no longer sent :frowning: or sent sometimes, on some Internet connections only