Note that this is an upgrade for the major release of postifx. Follow the
instructions for upgrading as stated in
http://de.postfix.org/ftpmirror/official/postfix-2.8.17.RELEASE_NOTES
Especially note the release notes stating:
If you upgrade from Postfix 2.7, or from Postfix 2.8 before July
25, 2010, you must execute "postfix reload" (or "postfix stop"
followed by "postfix start"). This is needed because the queue
manager to delivery agent protocol has changed. Failure to do this
results in repeated logging of warnings with:
warning: unexpected attribute rewrite_context ...
