Bernd Wurst wrote:

IMHO forwarding is not a problem. Although I admit I had to amend a few scripts, typically adding a "-f simp...@example.com" in the relevant command line, where <simp...@example.com> is delivered to the person who can remove that command line (me, in my case).

When a forwarding fails, I just remove it. If a DSN is required I send it manually. In facts, I have no automated methods to add forwarding rules.

The problem is for sites who can add lots of forwarding rules automatically. They must be able to also remove them automatically when they fail. SRS lends a technique for passing a unique bounce number. Receiving a bounce should remove the failed forwarding rule, besides forwarding the bounce to the original recipient: better design that carefully. Hence, although SPF apparently complicates life for mass forwarders, it also forces them to work sensibly.

Yes, people cannot illegally forward foreign messages. That is consistent with European privacy rules.

It helps the owner of a domain to avoid that others abuse of it.

Its relevance as an anti-spam device is to force spammers to send from their own domains, so that receivers know where they may claim damages. (Which will only happen when all hosts have SPF records)