If you're finding that recipients are being taken to an "...down for maintenance" page after clicking a trackable link in Soapbox Mailer, here's a few troubleshooting steps you can take to correct this situation.
1) Confirm that your Soapbox Mailer Site is active
Go to Setup > Develop > Site > Soapbox Mailer Email Tracking, and ensure that the Active checkbox is checked. If not, check it.
Happy emailing!