Sent email sync problems

Hi there, I am trying to replace outlook in my Company with a new email client,

I successfully imported all my emails and exchange server settings but I am having issues with the sync of the sent mail folder: it doesn’t sync and I always get the following error:

11:05:36   MailClient.Storage.Application.OperationException: La sincronizzazione della cartella ‘MYEMAILADDRESS/Posta inviata/’ è fallita a causa del seguente errore: Content conversion failed., Content conversion: Body conversion failed. —> Microsoft.Exchange.WebServices.Data.ServiceResponseException: Content conversion failed., Content conversion: Body conversion failed.

Please advise, I really love this app and I would love to use it!