cache ham setting should *not* inherit from @.

[dmorton]

Since the @. represents outgoing mail, it usually does not cache ham; this setting should not be inherited on new domains or users, as implemented for #323

[rjl]

Just as an additional note, maia_users.discard_ham really shouldn't be inheritable at all. Period. Just as most sites want to disable caching of outbound ham, some admins will want to do the same with ham aimed at domain-default accounts, and if they do that they'll end up passing along that setting to new users in their domains. Since those users won't have any way to enable/disable the setting for themselves (no interface control is provided at the user level), we'd be right back to forcing admins to make manual database changes to fix things.

In truth, we should also add a per-user control to the Settings page, so that users can decide on an individual basis whether they want ham to be cached. Much as disabling ham caching is undesirable in most cases, denying users the option may be worse.

[rjl]

Fixed in [1099], where maia_users.discard_ham is removed from the inheritance chain altogether. The maia_users table default (in maia-mysql.sql and maia-pgsql.sql) stipulates the discard_ham column will be set to 'N', the way it was prior to [1098].