Проверьте параметры,у меня все нормально работает.
Код:

$Body = gps | Out-String
$EmailFrom = "sergey.boris@gmail.com"
$EmailTo = "myname@yandex.ru"
$Subject = "List of Processes"
$SMTPServer = "smtp.gmail.com"
$SMTPClient = New-Object Net.Mail.SmtpClient($SmtpServer, 587)
$SMTPClient.EnableSsl = $true
$SMTPClient.Credentials = New-Object System.Net.NetworkCredential("sergey.boris", "Pa$$w0rd")
$SMTPClient.Send($EmailFrom, $EmailTo, $Subject, $Body)
$ou =new-object -com outlook.application
PS > $ou.GetNamespace("Mapi").GetDefaultFolder(6).items | select -skip 1 Subject,SenderName
Subject SenderName
------- ----------
List of Processes sergey.boris@gmail.com