{{tag>tutorial mail}}

====== Let postfix only accept mails for addresses in Exchange ======

===== Problem =====
  * I use postfix as a backup for my Exchange. I want postfix to only accept mail for recipients which exist in Exchange.

===== Requirements =====
  * I assume you followed my first tutorial [[tutorial:mail:postfixredir|here]]
  * Existing postfix installation (mine is on debian)
  * Existing Exchange (2010 or 2013) installation

----

===== Step 1 =====



  * Create the following PowerShell script on your Exchange server:
  * <code>
$ExcludeUsers = @("Administrator", "user1")

Add-PSSnapin Microsoft.Exchange.Management.PowerShell.E2010

# Get all valid recipients, excludes DiscoverySearchMailbox and every user alias included in ExcludeUsers
$ValidRecipients = Get-Mailbox | where {$_.Alias -NotLike "DiscoverySearchMailbox*"} | where {$_.Alias -NotIn $ExcludeUsers}
foreach ($Address in $ValidRecipients.EmailAddresses)
{[string]::Format("{0}`tOK", $Address.AddressString)}
</code>
  * Run the script and save the output to a file like this: ''%%./script.ps > output.txt%%''

----

===== Step 2 =====
  * Connect to yout server running postfix
  * Upload the scriptoutput to /etc/postfix/relay_recipients
  * Add the following lines to your /etc/postfix/main.cf:
  * <code>
relay_recipient_maps = hash:/etc/postfix/relay_recipients
show_user_unknown_table_name = no
</code>
  * Reload or restart postfix

----

===== Step 3+ =====
  * If your addresses change (added new or removed some) you have to repeat step 1 and 2