Yea mxtoolbox is what I use too. And you're right that ip address is not blacklisted however that's not the ip address that was listed in the email bounce backs the clients have been getting, and that is still blacklisted, when I checked this afternoon. It was another Vodafone ip address. I assume this is because they have more than one actual smtp server.
Thanks for recommending our Monitoring Tool, it can also auto alert you for any TCP, HTTP, or server issues as well! We'd like to echo the statement that if email is important to you, you may consider implementing a 3rd party service. We do offer Business email services that include SMTP Services, so keep that in mind.