In Tweak (or Exim) settings it would be great to enable / disable some of the e-mail features globally by default; after creation, the customer or server-admin could change or disable them on each account if needed.
[X] Enable SpamAssassin by default on new accounts [edit default settings]
[X] Enable SPF by default on new accounts [edit default settings]
[X] Enable DomainKeys by default on new accounts
I believe that the SpamAssassin is already there, but just so you get my point