This article explains what to do when you try to send a message to a Virginia Tech Google Workspace (Gmail) Mail address, and you receive the error message "550- This domain is blacklisted, consult your postmaster."'
Example: A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: ABC@vt.edu SMTP error from remote mailer after MAIL FROM:
Contact 4Help at http://4help.vt.edu and copy and paste the error message that you are receiving when you send messages to or receive messages from a Virginia Tech account. Also include the full headers of the email that contains the error message. For instructions on obtaining the headers, see Finding Email Headers.
If you use an email client to access your Virginia Tech Gmail while off campus and experience problems, use a Web browser instead of the client by following the instructions at Accessing Virginia Tech (VT) Gmail in a Browser.
If your domain is not being blocked, it is possible that your Internet Service Provider (ISP) is using a reverse Domain Name Server (DNS) pointer or using a mail relay. Ask your email or site administrator to set up the reverse DNS pointer or mail relay.
If you have breached the Acceptable Use Guidelines, you may appear on the Restricted Users List of Exchange Online. To restore your ability to send emails visit Restore Ability to Send Email in Exchange Online (vt.edu).