Senderbase.com is a new service from IronPort (an anti-spam company) that offers a peak into who the big online mailers are, including estimates on how much mail is coming from each company.

Of course there is a hidden implication in a lot of Ironport’s language that just because someone sends a lot of mail they should therefore be filtered out and can’t be permission-based or welcome in users’ in-boxes.

The arms race between legitimate mailers and ISPs seems to be escalating.