Random connection errors between EWS Java API 1.1 and https://podxxxxx.outlook.com/ews/Exchange.asmx

Question

I am sending email using connection setup as in subject. I have to send attachments. Code works but I am getting two errors at random times:

[java] INFO: Failure authenticating with BASIC ''@podxxxxx.outlook.com:443
[java] Error occured while sending the mail for: x@y.com
[java] microsoft.exchange.webservices.data.HttpErrorException: The remote server returned an error: (401)Unauthorized
[java] at microsoft.exchange.webservices.data.ServiceRequestBase.validateAndEmitRequest(Unknown Source)

or more often:

[java] microsoft.exchange.webservices.data.ServiceResponseException: An internal server error occurred. Try again later.
[java] microsoft.exchange.webservices.data.ServiceResponse.internalThrowIfNecessary(Unknown Source)

Any suggestions?