Microsoft.Exchange.WebServices.Data.ServiceResponseException: The mailbox does not have SMTP address associated with it.

[dkekesi]

When trying to find folders on an Exchange 2016 server, I get this error:
System.AggregateException: One or more errors occurred. ---> Microsoft.Exchange.WebServices.Data.ServiceResponseException: The mailbox does not have SMTP address associated with it.
at Microsoft.Exchange.WebServices.Data.ServiceResponse.InternalThrowIfNecessary()
at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.Exchange.WebServices.Data.ExchangeService.d__20.MoveNext()
The mailbox works, I can send mails to it.
I tried to find the exception message in the code, but I couldn't. Do you know what may cause this issue?

[dkekesi]

The mailbox does not have SMTP address associated with it. ErrorNonExistentMailbox 0

This is the response produced by the trace. This also has the error message, so it seems that the server is producing the error.