fredjhh,
If you wish to contact a forum member, simply click on the user name next to their post. This will give several options, one of which is "send a private message". A private message or PM is similar to a normal post, but received only by the intended recipient. The recipient is notified of a new PM when visiting the forum and (I believe) by email.
There is also an option to email. This will go directly to the address they have registered with the pprune forum and you do not need to know it beforehand.
I am enjoying your posts, by the way.
Hope this is of some help.