通过交换发送电子邮件失败

Question

我找不到在发送电子邮件时遇到问题的任何地方，这只发生在某些用户身上，而对于其他用户，一切正常都可以使用此代码进行操作：

 Dim service As New ExchangeService(requestedServerVersion:=ExchangeVersion.Exchange2013_SP1)
    Sub SendMail(ByVal Mailadressen As List(Of String), ByVal CCAdressen As List(Of String), ByVal Betreff As String, ByVal MailText As String, ByVal Anhang As List(Of String), Optional ByVal Absender As String = "")
        
        service.Url = New Uri("https://mail.server.com/ews/exchange.asmx")
      


        'Add a valid user credentials  
      
        service.Credentials = New WebCredentials("someuser", "somepasw", "somedomain")
       

        'To address the SSL challenge 
        ServicePointManager.ServerCertificateValidationCallback = New RemoteCertificateValidationCallback(AddressOf ValidateCertificate)

        Try            'Create new message object and set properties required to send a mail 

            Dim sender As New Microsoft.Exchange.WebServices.Data.EmailAddress
            Dim message As EmailMessage = New EmailMessage(service)
            message.Subject = Betreff
            message.Body = MailText

            If Absender <> "" Then
                Absender = Absender
                sender.Address = Absender
                message.From = sender
            End If

            For Each adr As String In Mailadressen
                message.ToRecipients.Add(adr)
            Next


            For Each cc As String In CCAdressen
                message.CcRecipients.Add(cc)
            Next

            For Each a As String In Anhang
                message.Attachments.AddFileAttachment(a)
            Next

           
            message.SendAndSaveCopy()
          
        Catch ex As Exception
            MessageBox.Show(vbNewLine & "" & vbNewLine & String.Format("Error: {0}", ex.StackTrace))
        End Try

    End Sub

我遇到的错误：

在Microsoft.Excange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse （IEwsHttpWebRequest请求）在 Microsoft.Excange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest （IEwsHttpWebRequest和请求 .WebServices.Data.ExchangeService.InternalCreateItems（Inumerable1 项目，FolderId，parentFolderId，NUllable1 messageDisposition， NUllable1 sendInvitationsMode，ServiceErrorHandling errorHandling）位于 Microsoft.Excange.WebServices.Data.Item.InternalCreate1 messageDisposition1 .WebServices.Data.EmailMessage.InternalSend （FolderId parentFolderId，MessageDisposition messageDispostition）

您能给我一些建议吗，这可能是问题所在吗？非常感谢