[System.Reflection.Assembly]::Load("Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c") | out-null  
[void][System.reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")  
 $oContentService = [Microsoft.Sharepoint.Administration.SPWebService]::ContentService;  
 [Microsoft.SharePoint.Administration.SPWebApplicationCollection]$waColl = $oContentService.webApplications;  
 $waColl1 = $waColl | where-object {$_.IsAdministrationWebApplication -eq $FALSE}  
 write-host "WebApplication; Site Collection; List Title; List URL; EmailAlias" 
 foreach ($wa in $waColl1)  
 {  
 $sites = $wa.Sites  
 foreach ($obj in $sites)  
 {  
 $spSite = new-object Microsoft.SharePoint.SPSite($obj.URL)  
 $colWebsites = $spSite.AllWebs  
 foreach ($web in $colWebsites)  
 {  
 $colLists = $web.Lists  
 foreach ($list in $colLists)  
  {  
  if ( $list.EmailAlias -ne $null )  
  {  
  write-host  $wa.Name, ";", $obj.URL, ";", $list.Title , ";", $list.DefaultViewUrl, ";",  $list.EmailAlias  
 $a = $list.EmailAlias
 $a
 $list.Emailalias = $a
 $list.update()
 }  
 }  
 }  
 }  
 }  
 write-host "Finished."

$site = Get-SPWeb <URL of the sub site>
$list = $site.Getlist("<URL of the list")>
$a = $list.EmailAlias
$a
$list.Emailalias = $a
$list.update()