Send-MailMessage throw error and send the email

[EliadTech]

Steps to reproduce

Run Send-MailMessage with CC or BCC, but without TO, and with BodyAsHTML.

Expected behavior

Either throw error and break (because TO is empty) or send the email (to CC or BCC) without an error.

Actual behavior

You get an error that the email address is invalid and the email is sent but empty.

Environment data

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      5.0.9740.0
WSManStackVersion              3.0
SerializationVersion           1.1.0.1
CLRVersion                     4.0.30319.34014
BuildVersion                   6.3.9740.0
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.2

[SteveL-MSFT]

Just tried this on PS5.1 and can't replicate as TO cannot be empty

PS C:\Users\slee\repos\PowerShell> Send-MailMessage -Cc foo@bar.com -BodyAsHtml

cmdlet Send-MailMessage at command pipeline position 1
Supply values for the following parameters:
From: test@test.com
Subject: test
To[0]:
Send-MailMessage : Cannot validate argument on parameter 'To'. The argument is null, empty, or an element of the
argument collection contains a null value. Supply a collection that does not contain any null values and then try the
command again.
At line:1 char:1
+ Send-MailMessage -Cc foo@bar.com -BodyAsHtml
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidData: (:) [Send-MailMessage], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.SendMailMessage

[EliadTech]

That's because you left BodyAsHtml empty.
I've just tested it again on PS 5.1.
Try this:
Send-MailMessage -Cc foo@bar.com -BodyAsHtml 'Blablabla' -smtpserver exchange.bar.com -subject test -from tester@bar.com

[dayroncj]

For future readers...

The error is because "-To" parameter cant be null or empty. If the intend is to use "-Bcc" rather "-To", you can use a dummy email address like 'noreply@noreply.com' and set the "-Bcc" paramter with all the recipients.

For last, -BodyAsHtml is a boolean parameter thus no value is neccesary.

[ThreeFive-O]

To summarize the issue:
The cmdlet was used in a wrong way where the Boolean switch -BodyAsHtml was used in a similar fashion like -Body.
Since the switch -BodyAsHtml takes no input object, the positional parameters kicks in. As all other parameters are named, the first positional parameter will be -To.
Hence the provided sample call

Send-MailMessage -Cc foo@bar.com -BodyAsHtml 'Blablabla' -smtpserver exchange.bar.com -subject test -from tester@bar.com

could be written as

Send-MailMessage -Cc foo@bar.com -BodyAsHtml -To 'Blablabla' -smtpserver exchange.bar.com -subject test -from tester@bar.com

Input 'Blablabla' can be bound to parameter -To as it is of type string. No problem occurs during binding.
Later the string values for -To,-Cc and -Bcc are checked for correct format. This happens in the following lines of code in Send-MailMessage:

PowerShell/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Send-MailMessage.cs

Lines 286 to 319 in 1abf290

	private void AddAddressesToMailMessage(object address, string param)
	{
	string[] objEmailAddresses = address as string[];
	foreach (string strEmailAddress in objEmailAddresses)
	{
	try
	{
	switch (param)
	{
	case "to":
	{
	_mMailMessage.To.Add(new MailAddress(strEmailAddress));
	break;
	}
	case "cc":
	{
	_mMailMessage.CC.Add(new MailAddress(strEmailAddress));
	break;
	}
	case "bcc":
	{
	_mMailMessage.Bcc.Add(new MailAddress(strEmailAddress));
	break;
	}
	}
	}
	catch (FormatException e)
	{
	ErrorRecord er = new ErrorRecord(e, "FormatException", ErrorCategory.InvalidType, null);
	WriteError(er);
	continue;
	}
	}
	}

It can be seen that in Line 315 an error is written, but the cmdlet won't terminate because of this error.

Ultimately the mail will be sent, though the "To" member of the _mMailMessage object is empty.

Possible solutions:

1. Make cmdlet parameters for -To,-Cc and -Bcc of type System.Net.Mail.MailAddress. This would perform a format check right away and abort the action if not all provided email addresses are valid.
   This definitely would be a breaking change, since the current behavior allows invalid mail addresses to be specified, where PS will provide an error, but the mail could still be sent to all other addresses.
   This current behavior can be convenient if you have a list of email addresses, but at least one mail address is not in the correct format, e.g.

Send-MailMessage -To valid@test.com, notvalid@ ...

The email would still be sent to all valid addresses.

2. Validate that -To at least has one valid email address if addresses in -Cc and/or -Bcc are given. Easily spoken, the property "To" of _mMailMessage is not allowed to be empty.

[adityapatwardhan]

@ThreeFive-O Thanks for the detailed analysis. Can this issue be closed since, the cmdlet is behaving as expected?

[ThreeFive-O]

@adityapatwardhan In my opinion this issue can be closed. But another issue or PR should be made to improve the user experience when using non-valid email addresses in -To, -Cc and -Bcc.
It's on my To-Do, but other PRs for this cmdlet are more important, which I want to fix first.