I have been successfully using Sendgrid through Azure to send critical system updates to my clients for some time. All of my emails have suddenly started to become 'Deferred' before either being sent or blocked. I've done some research and there is a chance that my email address has been put onto a Blacklist. All of the emails sent are just, and are in no way spam.
How do I check if I'm on a blacklist and resolve the issue? I know that there are sites out there but I don't want to sign up for any scam services.