Powershell Sendmail GMail

$SmtpClient = new-object system.net.mail.smtpClient
$SmtpClient.Host = "smtp.gmail.com"  
$SmtpClient.Port = 587
$SmtpClient.EnableSsl = $true
$SmtpUser = "xxxxxxx@gmail.com"  
$SmtpPW = "xxxxxxxx"  
$SecPW = $SmtpPW | ConvertTo-SecureString -AsPlainText -Force
$Credential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $SmtpUser, $SecPW
$SmtpClient.Credentials = $Credential
                                              
$MailMessage = New-Object system.net.mail.mailmessage

$MailMessage.SubjectEncoding = $utf8
$MailMessage.from = $SmtpUser
$MailMessage.To.add("xxxxxxxxx@xxxxxx.de")  
$MailMessage.Subject = "Benachrichtigung”  
$MailMessage.IsBodyHtml = $true  

$attachment = new-object system.net.mail.attachment($Dateiname)

$attachment.ContentDisposition.Inline = $True
$attachment.ContentDisposition.DispositionType = “Inline”
$attachment.ContentType.MediaType = “image/jpeg”
$attachment.ContentId = ‘image1.jpg’

$MailMessage.Attachments.Add($attachment)
$SmtpClient.Send($MailMessage)

109 |  $SmtpClient.Send($MailMessage)
     |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     | Exception calling "Send" with "1" argument(s): "The SMTP server requires a secure connection or the  
     | client was not authenticated. The server response was: 5.7.0 Authentication Required. Learn more at"