Problem

You perform a database attach upgrade from a 2007 farm to a 2010 farm. You decide that you want to use a different URL for the web application. After performing the upgrade, you realise that all the alerts on the web application still use the old SharePoint URL.

Solution

Use a powershell script to update the alert URL in your entire web application.

get-spsite -limit all -WebApplication http://portal | get-spweb -limit all
|ForEach-Object {$_.alerts|foreach-object{$_.properties[“siteUrl”] =
“http://portal”;$_.update()}}