Depending on your mail service provider, if they have a web interface/app, you should be able to add a filter to block the domain suffix. My email app (bluemail) allows me to add to my block list sender or domain or suffix, which is supplemental to your mail server's block list. You might look in your mail app's settings to see if you have a similar setting. It may be hidden/hard to find. Or, you may want to consider switching.
