when is a reply-eMail succesfully fed into the original thread?

Hello,

I have set up a couple of forums, now, and I am pretty satisfied with nabble's functionality.

Just some things concerning the eMail-reply-function seem not clear to me at this point.


TECHNICAL CRITERIA FOR SUCCESFUL REPLY
When user [A] posts a new message into a forum (or sub-forum), where user [B] subscribed for eMail notification, user [B] will get [A]'s new message via eMail and can read and reply using his standard eMail client. When user [B] replies to this message via eMail, [B]'s message is not necessarily posted as a new message back into the original forum. Occasionally, a new topic is opened with the replied message.

Here is what I tried as the technical prerequisites for [B]'s reply eMail to be fed back into the original forum. But, as I said, this does not seem to work stable for all users and their eMail clients:

(1) the eMail address registered in the forum has to be the same as the one replying the eMail
(2) the recipient eMail address has to be the one provided by the original eMail as reply address
(3) the subject line of the reply eMail can hold a "Re:" as an added prefix
(4) the rest of the subject line of the reply eMail must correspond the the original message title


questions:

-> are there other prerequisites? Maybe somehow (invisibly) coded within the eMail file?
-> would it be possible to use some other prefix (e.g. "Aw:" or "RE:" or just nothing) instead of "Re:"?


Thank you.