Email archiving I think is a growing market, we have some customers using GFI Mail Archiver.

I think 'out sourced' email archiving would be good to sell in as an additional service. And who better to archive inbound/outbound emails than your email gateway/ISP? 

The service could be sold as an optional extra to clients on a per account, per email, or total storage space (or a combination of)? I think the feature should allow for storage of emails in a separate database to SF, and possibly even multiple databases on a per domains basis to spread storage for domains across various servers. A web interface for searching users archives on a per user/domain/customer basis, with a forwarding option.

What do you think?