If you are wondering why you get PPRuNe emails notifying you of the latest post, then you need to amend your Options.
Go to your User CP > Edit Options and change the default
(see picture) to something other than "Instant email notification".
After you have done this, you might need to "Unsubscribe" from threads that you have posted to, because VBulletin "remembers" previous threads you have "subscribed" (posted) to.
DT