Problem with Sending Mail from a Cloud Server

Ever since I migrated to a cloud server, I had not received the occasional emails from my sites. Until today when I was expecting a email from one of the sites. I waited and no mail comes through, I triggered few more re-sends, but none made it to my inbox.

After some researching, it turns out that most cloud servers' IP's (if not all) are by default "blocklisted" by Spamhaus. I am pretty upset that there is such thing and it is not more widely known. Their reason is to prevent spammers from using cloud servers, given that cloud servers can be easily obtained in volume. At least Spamhaus makes it fairly easy to look-up/remove your blocked IP's.

Solution: Go to look-up your IP and request a removal. After about 30 minutes, mails were able to be sent from my cloud servers once again.