Param(
[string] $ContainerDN,
[string] $Database = "",
[bool] $append = $false
)

#function to validate input parameters
function ValidateParams
{
$validInputs = $true
$errorString = ""

if ($ContainerDN -eq "")
{
$validInputs = $false
$errorString += "`nMissing Parameter:  The -ContainerDN parameter is required. Please pass in a valid container in which to create the user accounts."
}

if (!$ContainerDN.Contains(","))
{
$validInputs = $false
$errorString += "`nInvalid Container DN.  Make sure to enclose the entire DN in double quotes or it will not be parsed properly."
}

if (!$validInputs)
{
Write-error "$errorString"
}

return $validInputs
}

#function to get the display name and alias from mailbox data in the Exchange store
function ExtractDisplayNameAndAlias($obj)
{
[string[]]$legacyDNSplit = $obj.LegacyDN.Split('/')
$alias = $legacyDNSplit[$legacyDNSplit.Length-1].Remove(0,3).ToLower()
$output = "dn: CN=" + $obj.DisplayName + "," + $ContainerDN + "`r`nchangetype: add`r`nuserAccountControl: 544`r`nmsExchUserAccountControl: 0`r`npwdLastSet: -1`r`ndisplayName: " + $obj.DisplayName + "`r`nobjectClass: user`r`nsAMAccountName: " + $alias + "`r`n"
write-output $output | out-file -filePath "c:\ldifout.ldf" -append -noClobber
}

# Function that returns true if the incoming argument is a help request
function IsHelpRequest
{
param($argument)
return ($argument -eq "-?" -or $argument -eq "-help");
}

# Function that displays the help related to this script following
# the same format provided by get-help or <cmdletcall> -?
function Usage
{
@"

NAME:
CreateLdifFromDisconnectedMailboxes.ps1

SYNOPSIS:
Finds all disconnected mailboxes on the local server and creates an LDIF file 
with an entry for each disconnected mailbox user. Use the LDIFDE utility to import this LDIF file to Active Directory, which generates the user accounts. You can then reconnect Mailboxes 
to these accounts by using the Connect-Mailbox cmdlet. You can
specify a particular database, or specify no database to search all databases
on the local server.

This script is mainly used for disaster recovery scenarios where all data except  
the mailbox databases have been lost.  In these scenarios, without a backup of Active
Directory, you must re-create the user accounts so they can be 
connected to existing mailboxes. This is the main objective of this script.

SYNTAX:
CreateLdifFromDisconnectedMailbox -ContainerDN <AD Container DN> 
-Database <Identity of Database> -Append `$false|`$true

AD Container DN is a valid Active Directory container in distinguished name format. This value
must be enclosed in quotes. Database is the Identity parameter of the 
database. You can retrieve the Identity value for all databases on the local 
server by running the following cmdlet:

get-mailboxdatabase -server Server01 | fl Identity

Setting -append to `$true tells the script to append data to the current 
c:\ldifout.ldf file instead of overwriting it. This is the recommended
setting if you are piping output from other cmdlets to this script. If the
-append switch is not included, the script runs automatically in overwrite mode.

EXAMPLES:

"Specifying Database ID"
CreateLdifFromDisconnectedMailbox -ContainerDN "CN=Users,DC=Domain,DC=com" 
-Database "SERVER\Storage Group\Database"

"Run Against All Stores on Local Server"
CreateLdifFromDisconnectedMailbox -ContainerDN "CN=Users,DC=Domain,DC=com" 

"Pipe output of another cmdlet into this script"
get-mailboxdatabase -server SERVER | foreach {CreateLdifFromDisconnectedMailboxes -ContainerDN 

"CN=Users,DC=domain,DC=com" -Database `$_.Identity -append `$true}
"@
}

################################################################
##########################BEGIN SCRIPT##########################
################################################################

#Check if this is a help request
$args | foreach { if (IsHelpRequest $_) { Usage; exit; } }

#Delete existing LDIF file if it is there and append is set to false
if(!$append){$a = remove-item c:\ldifout.ldf -ea SilentlyContinue}

#Validate all input parameters
$ifValidParams = ValidateParams;
if (!$ifValidParams) { exit; }

#find all disconnected mailboxes and get required information
if ($Database -ne "")
{
write "Getting disconnected mailboxes for database $Database"
$getmbxcmd = get-mailboxstatistics -Database $Database | where {$_.DisconnectDate -ne $null}
}
else
{
write "Getting disconnected mailboxes for all databases on local server."
   $getmbxcmd = get-mailboxstatistics | where {$_.DisconnectDate -ne $null}
}

#Make sure at least one disconnected mailbox is found; if not, exit script
if ($getmbxcmd -eq $null) {write "No disconnected mailboxes found.";exit}

#loop through each disconnected mailbox and write entries to the output file
foreach ($entry in $getmbxcmd)
{
ExtractDisplayNameAndAlias $entry
}

write "LDIF file successfully written to C:\ldifout.ldf."

CreateLdifFromDisconnectedMailboxes -ContainerDN "<DN of container to place users>"

CreateLdifFromDisconnectedMailboxes -?

Get-MailboxStatistics | Where {$_.DisconnectDate -ne $null} | Connect-Mailbox -Database "Server01\SG1\MBX1"