$FileDate = Get-Date
$SmtpServer = 'smtp.office365.com'
$SmtpUser = 'blah@blah.com'
$smtpPassword = 'blah'
$MailtTo = 'blah@blah.com'
$MailFrom = 'blah@blah.com'
$MailSubject = "The file for $FileDate is attached."
$MailBody = "Please take action"
$attachment= "C:Usersmy usermyfile.txt"
$attach = new-object Net.Mail.Attachment ($attachment)
$Credentials = New-Object System.Management.Automation.PSCredential -
ArgumentList $SmtpUser, $($smtpPassword | ConvertTo-SecureString -
AsPlainText -Force)

Send-MailMessage -To "$MailtTo" -from "$MailFrom"  -Subject $MailSubject -
Body $MailBody -SmtpServer $SmtpServer -UseSsl -Credential $Credentials -
attachments "$attach"

Send-MailMessage : Could not find file
'C:UsersmyuserSystem.Net.Mail.Attachment'.
At line:1 char:1
+ Send-MailMessage -To "$MailtTo" -from "$MailFrom"  -Subject $MailSubject -
Body $ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Send-MailMessage],
FileNotFoundException+ FullyQualifiedErrorId :
System.IO.FileNotFoundException,Microsoft.PowerShell.Commands.SendMailMessage