Mandatory and default parameters of a function - function

Question

I have written a little PowerShell send-email-function for a special purpose (error-message) so that the from and to addresses are always the same!
Function Send-EMail {
Param (
[Parameter(Mandatory=$true)] [String]$EmailTo = "ToAddr#gmx.at", # default
[Parameter(Mandatory=$true)] [String]$EmailFrom = "FromAddr#gmail.com", #default
[Parameter(Mandatory=$true)] [String]$Subject,
[Parameter(Mandatory=$true)] [String]$Body,
[Parameter(mandatory=$false)] [String]$Attachment,
[Parameter(mandatory=$true)] [String]$Password
)
$SMTPServer = "smtp.gmail.com"
$SMTPMessage = New-Object System.Net.Mail.MailMessage($EmailFrom,$EmailTo,$Subject,$Body)
if ($attachment -ne $null) {
$SMTPattachment = New-Object System.Net.Mail.Attachment($attachment)
$SMTPMessage.Attachments.Add($STMPattachment)
}
$SMTPClient = New-Object Net.Mail.SmtpClient($SmtpServer, 587)
$SMTPClient.EnableSsl = $true
$SMTPClient.Credentials = New-Object System.Net.NetworkCredential($EmailFrom.Split("#")[0], $Password);
$SMTPClient.Send($SMTPMessage)
Remove-Variable -Name SMTPMessage
Remove-Variable -Name SMTPClient
Remove-Variable -Name Password
Remove-Variable -Name Body
Remove-Variable -Name Subject
} #End Function Send-EMail
....
$subj = "Subject"
$body = #" Body-Text "#
Send-EMail -Subject $subj -Body $body -Password "myPWD" -Attachment $logFile
I expect now that I don't have to specify again the email address, but if run it line by line in the ISE debugger a little window is opened asking me for the EmailTo address:
What do I have to change so that I am not asked for the already given addresses?

Answer 1

The Mandatory parameter attribute flag:
[Parameter(Mandatory=$true)]
really means "It is mandatory for the caller to supply an argument to this parameter".
If you want a parameter to fall back to a default value that you provide in the param block, set the Mandatory flag to $false:
[Parameter(Mandatory=$false)]
[string]$EmailTo = "to#company.domain",
This may seem a little counter-intuitive, but it allows you to detect when a user didn't supply a parameter that is needed:
if(-not($PSBoundParameters.ContainsKey('EmailTo')) -and $EmailTo)
{
# User relied on default value
}