Further to the above, it would of course be possible for more than one person to use the same user name. For example there is nothing to stop someone else registering at another forum using your user name, but they could NOT use your e mail address. Have I understood your question properly?
Marg7 is right, I am suggesting someone is spoofing my email address to send emails to me; the resultant problem is that I cannot delete them as spam as my email provider would then send ALL emails addressed to me straight to the Spam folder!
I have changed my password by the way, but that will not stop spammers sending emails to my email address!
"From a little googling, it seems that nothing can be done...."
That's correct. All you can do is change your email address. However spammers can still keep on spoofing you old one.
The more unlikely your email address, the less likely it is to be auto-spoofed (my invented word) - this is where spammers simply guess your name, as in they spoof as dave1, dave2, dave3, dave4 etc etc