Using @ character in exchange powershell remoting (2010)

vlciho 

I would recommend you to set complete commands in one string variable and use AddScript function to add the string text as commands

Dim strScript As String = "Set-MailPublicFolder -Identity '"+strIdentity+"' -GrantSendOnBehalfTo @{add= "+ _username +" }"
Dim R2 As System.Management.Automation.Runspaces.Runspace = System.Management.Automation.Runspaces.RunspaceFactory.CreateRunspace(pConnectionInfo)
R2.Open()
Dim P2 As System.Management.Automation.Runspaces.Pipeline = R2.CreatePipeline()
P2.Commands.AddScript(strScript);
Dim results As Collection(Of PSObject) = P2.Invoke()
R2.Close()

For your case, the string text should be like below :

Dim strScript As String = "Set-MailPublicFolder -Identity Set-MailPublicFolder -Identity 'CN=PF1,CN=Microsoft Exchange System Objects,DC=xxxxxxx,DC=local' -GrantSendOnBehalfTo @{add='domain\john.doe'}"