If you're having trouble sending a group of people in the same company or unable to receive your own send test, it is likely caused by email firewalls. It is suspicious that multiple people in the company receive same email from same sender at the same time. In this case, you may want to send this page to their IT administrator and politely ask them to whitelist our IP addresses. This way hopefully can resolve the deliverablity issue.
Our Delivery IPs:
Below are the IP ranges we use to send emails: