If you have sent an email and received returned mail with the error "Service Unavailable" or "Your domain is banned" then that domain has blocked email from our domain.
Internet service providers may block email based on domains or IP addresses, and we currently block many domains. In the same respect, there are some domains that block us as well.
It is our policy to first notify any domain of our intent to block them, along with the specific reason. If that domain responds to us with more information concerning our complaint, we are generally able to resolve the issue without blocking.
Conversely, most domains will contact us regarding any spam or unsolicited commercial email coming from our domain. When we are contacted in this regard, we will immediately investigate their complaint and, if warranted, suspend or terminate the subscriber in question and communicate our actions to the domain who complained to us.
However, there are instances where a domain will not notify us of their intent to ban and simply ban us without giving us the opportunity to respond.
Contact us regarding the status of any domain we have banned or any domain that has banned us. You can also refer to the AT&T Block Inquiry Website
for more information on the the enforcement of our mail policies.