Thanks to both of you for this report. I was able to duplicate the issue this morning using my cox.net email account. When I clicked on the menu option within an email to "mark as spam", I received the following error:
"Message could not be sent to the following recipients: [spamreport@cox.net] (451 - 451 4.2.0 146.20.112.67 has exceeded the number of messages allowed per hour and has therefore been blocked for a period of three hours. If you have not been knowingly sending large volumes of email, this may indicate that your computer is infected with a virus which is sending emails without your knowledge. Please scan your system for viruses as soon as possible. The block will automatically be lifted at the end of the three-hour period. Please visit http://ww2.cox.com/coxagainstspam for more information."
Please provide the type of device you use to access your Cox email (PC, tablet, etc.), the device operating system, and browser version or app name. For example, I'm using a Windows 10 laptop, and I accessed Cox Webmail using Internet Explorer 11. I will get this reported at once!