Spam and how to stop it.

I'm not sure if this is the right place to post this but if not then apologies and may the mods move it to the relevant place and go in peace....amen!

In the past week I've suddenly started to receive 100+ emails per day all addressed to different people @ oceanfree.net but all arriving at my email address which is XXXXX @oceanfree.net

Now, the good people at oceanfree have told me to check the headers and block the emails which is all very well but when you have them coming form a hundred different adresses each day it gets difficult.

The one common theme in these is they all come through ontario.esatclear.ie or fizzbag.esatclear.ie or tweedledum.esatclear.ie

Is there any way to block anything coming through esatclear.ie without cutting off the genuine mails?

Is this the right way to go about it or is there some other route I could take?