How to reply to posts

How should I reply to post from mailing list. I lost myself in replying 
via email, don't know what subject to put, to put Re: or not, and how to 
format it.

I used http://python.6.x6.nabble.com/PyQt-f1792048.html before and it 
worked ok and it was very practical, much better than email and better 
to follow. I had full view of all posts, just clicked on Reply and post 
a message. Now when I click to reply, I get the message "Authorized 
Users Only ... You can use the form below to send a request to the 
administrators." And I send request and nothing happens. Is there a way 
to post on nabble.com site anymore?

If not, how to post via email, not the first time, but post a reply? So 
far I used digest,clicked to Reply to all and deleted all other 
messages, but the format was lost and I forgot to change the subject 
from "PyQt Digest, Vol x, Issue y" to something else. How will 
nabble.com know it's the same thread?

Nenad