In
this article Google explains the concept of a Gmail Address Alias, as follows.
Using an address alias
Gmail doesn't offer traditional aliases, but you can receive messages sent to your.username+any.alias@gmail.com. For example, messages sent to jane.doe+notes@gmail.com are delivered to jane.doe@gmail.com.
You can set up filters to automatically direct these messages to Trash, apply a label or star, skip the inbox, or forward to another email account.
I may be missing something very fundamental here, but it would seem pretty clear that all a spammer (program) has to do to get the 'real' Gmail address is to remove the
+notes from the above example to obtain
jane.doe@gmail.com. In general, just remove everything from the
+ to the
@gmail.com, including the
+.
If so, what on earth is the point of Gmail aliases? I'm deeply puzzled...