| > Many ISPs run filters on all incoming mail. Sometimes, forwarding takes
| > place because of infrastructure changes, system changes, etc., on a
| > per-domain basis, especially in a managed messaging environment. Resent
| > headers should not be inserted because of these system-wide,
| system-imposed
| > filtering rules.
|
| I would not expect Sieve to be used in these cases. Existing methods
| (for example, .forward) would be used. Sieve is for conditional,
| message-based actions, during final delivery, on behalf of users.
An example: When one of several domains of users is moved from one mailer to
another, during the migration phase the former will forward mail to the
latter, on a system-wide basis. Using .forward features, or other per-user
features is neither convenient nor very efficient.