Recently a client sent out an email with a bad link in it. Normally, I'd sympathise with them but tell them that the horse has bolted and there's no point in closing the barn doors (because I like to use old fasioned expressions). (And yes - if the link was on my server, I could give them an apache redirect.) But, if the message went out via civimail and you're tracking click-throughs of links (actually this trick also works with simplenews if you're using simplenews_stats), then there's still hope. This is because the actual link embedded in the mail isn't the final destination, but a civicrm url with a magic trackable url id, which then redirects to the final url, which is stored in a civicrm table. The rest you can probably do as a simple homework exercise, but here's the details since I've got more room for this post. Start with loading up a mysql client and use your civicrm database, then find out the right id using this: select * from ci...