From my own experience, research and my interaction with Mimecast and Email Systems(British Academy), more and more commercial email providers are not just doing the usual html and content check, they are focussing more on the spam sender itself rather than the spam email.
They will have groups of safe-lists; global ones and personal ones. If the email coming in is not on any safe lists, emails will get put in a global or personal bulk folder or the email servers will ask the sending server to validate itself, like Mimecast.
I expect this to spread.
Hotmail will already put everything in the bulk folder that is not from a known contact.
More companies are using professional email providers rather than dealing with it in house I believe it's likely this will spread to internal email server software - ie exchange server etc or there will be pluggins.
Could this essentially kill off cold emails; Acquisition Campaigns etc.
Should we start getting our customers to put a now popular phrase in their emails:
"To ensure this email gets in your inbox please add this address to your email contacts list"
Obviously this is more newsletter related than anything else.
Should we therefore also try to get our customers to build there own lists. ie: listbuilder interface, web interaction, web focus community and forum actions etc.
What to do, what to do!