There is email notification of dialogues only for second and subsequent posts, not this initial one.

I think it is essential to have this feature on the first post too, because users don't know to check as do they when a dialogue has already been started (so in this sense the notification is more important for initial posts).

This has been mentioned by several people in the forums but hasn't been addressed yet. http://moodle.org/mod/forum/discuss.php?d=5826

I and others have been missing helping students due to being unaware of existing contacts from students, so this is a critical pedagogical issue.