Spammers employ a number or tricks to help evade the spam filters which all providers constantly adjust to try to eliminate as much as possible.
On a server level we block around 97% of all spam that hits our server and we're continually monitoring and working to improve how we manage spam, however it is a fine balance so that legitimate email is not also picked up in the sweep.
You can manually block a spammer by adding them onto the block list in your web mail platform.
To make it more effective instead of putting the entire email address (eg: george@mcspammy.com) in the block list, try adding just the domain to the block list (e.g. *@mcspammy.com). Add it in with the * before the @ symbol. This will then block all email coming from @mcspammy.com rather than just the single address.
Hopefully this will be more effective in blocking spammers. Please note: If you see emails coming from a sub-domain you would treat them as separate domains.
eg: george@spamalot.mcspammy.com
*@mcspammy.com wont block george@spamalot.mcspammy.com
likewise, *@spamalot.mcspammy.com wont block george@mcspammy.com