Does anyone have experience of hosted services for monitoring the status of email servers?
I host my own email on a Linux VPS. If either my SMTP or IMAP servers stop responding to requests, I want to receive an SMS within 10 minutes telling me so.
Better still, I'd like to be able to set up arbitrary TCP banner checks (i.e. periodically connect to a specified port and verify that it receives a specified string). I know that software exists that does this - monit, nagios, etc - but I don't want to host or maintain it myself.
Subscription services are fine (indeed I'd expect to pay something for this).