Unable to capture/redirect warning from Exchange cmdlet

Question

I am using trying to use the Set-DistributionGroup Exchange cmdlet in the following manner:

$Exch_Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri $ExchangeURI -Authentication Kerberos
Import-PSSession $Exch_Session -commandname Set-DistributionGroup -AllowClobber

if (<condition>) {
    try {
        Set-DistributionGroup @Setparams
    }
    catch {
        <error capture code here...>
    }
}

On success and failures, everything works as expected...But during a test run, while trying to change the PrimarySMTPAddress to an invalid value, I get a WARNING (not error) that the new email address doesn't adhere to an e-mail address policy so it will not be changed. But since this is a warning, the try/catch doesn't trigger and the entire process wrongly finishes as successful.

I've tried:

1. adding -WarningAction Stop to the command and that does trigger the try/catch, but the error is too generic:

   Command execution stopped because the preference variable "WarningPreference" or common parameter is set to Stop.

2. So I tried to capture the warning to a variable as well as file (to check for later when reporting success or failures), but all the ways I tried to capture failed, even though it continually displayed the warning to the screen.

   Set-Distributiongroup @Setparams -WarningVariable cmd_warn
   Set-Distributiongroup @Setparams 3> c:\temp\warnings.txt
   ...
   $command = "Set-Distributiongroup @Setparams"
   iex $command 3> c:\temp\warnings.txt
   

   But the file and variable are always empty, what am I doing wrong or missed?

Answer 1

You state that you're using Import-PSSession, which creates an (in-memory) module with proxy functions that transparently call commands of the same name on a remote machine, a concept known as implicit remoting.

Unfortunately, as of Windows PowerShell v5.1 / PowerShell Core 6.2.0-preview.4, the implementation of this feature has a number of problems with respect to preference variables, common parameters, and output streams.

In your specific case, try the following workaround:

Invoke-Command { Set-Distributiongroup @Setparams } -WarningVariable cmd_warn
if ($cmd_warn) { ... } # warning was emitted

Note that the Invoke-Command call here doesn't itself perform remoting; it is merely a local invocation wrapper that makes the -WarningVariable common parameter work when applied to it.