Random Microsoft 365 mailbox backups fail

Hello,

since end of January the same old random error while backing up Microsoft 365 mailboxes happens again:

Die .NET-Ausnahme 'System.Net.WebException' ist aufgetreten: Die zugrunde liegende Verbindung wurde geschlossen: Unerwarteter Fehler beim Senden.. Ausnahme-Stapelüberwachung: bei System.Web.Services.Protocols.WebClientProtocol.GetWebResponse(WebRequest request) bei System.Web.Services.Protocols.HttpWebClientProtocol.GetWebResponse(WebRequest request) bei System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters) bei ComEwsAdapter.ExchangeWebService.ExchangeServiceBinding.GetFolder(GetFolderType GetFolder1) bei MsExchange.Ews.ReTryStrategy.DoTry[TReturn,TArg](TCallDelegate`2 call, TArg arg) bei MsExchange.Ews.ReTryExchangeServicePoint.GetFolder(GetFolderType getFolder) bei MsExchange.Ews.ExchangeConnectionEngine.CheckConnection(IExchangeServicePoint service, RootObjectServicesProvider root) bei MsExchange.Ews.ExchangeServiceFactory.GetService() bei MsExchange.Ews.ExchangeConnection..ctor(String url, NetworkCredential user, RootObject root, ConnectionOptions options) bei MsExchange.Ews.ExchangeConnection..ctor(String url, Credentials user, RootObject root, ConnectionOptions options) bei MsExchange.Ews.ExchangeClient.ConnectToAsUser(String url, Credentials user, RootObject root, ConnectionOptions options, IExchangeConnection& connection)

If I run the backup 3 times, usually all mailboxes are save one time successfully, but per run meanwhile approximately up to 50% of the mailboxes fail.

This happened already in the last year and was fixed in November. (https://kb.acronis.com/content/69732)

Started with a few failing mailboxes, but is now untolerable.

Our cloud customers do not experience the same behavior.

Best greetings from Germany
Olaf