The mailbox one is bugged for me, all I have in the mailbox is the riding letter. I've clicked on all available NPC's and there is no quest to receive. I've done kill scarlet, gather arrows, win 5 duels and the quest for the mount. It seems that some people get the next quest and some people don't. Im not the only one stuck on lvl 61 in the starting zone... I made three new DK's and still can't get the quest. And also nothing in the mailbox except the riding letter.
I know this is an old thread but I ended up here earlier when I couldn't figure out how to advance the DK starting quest line. If you go to the mailbox and zoom your camera in a bit, you will notice a note/scroll thing. Click on THAT, and NOT the mailbox, and you can advance the quest! Hope this helps someone!
The mailbox is just a mailbox. Mailboxes can never ever in any way give quests (unless the attached item in a mail starts a quest, like the riding quest). The thing that gives the quest is the scroll on top of the mailbox. All you have to do is not be completely blind, notice the scroll with the giant yellow exclamation mark above it, right-click it and take the quest.
Apart from that (which is not even a bug or anything - just players having the attention and focus of a 5-year-old), the entire chain works normally.
I know this is an old thread but I ended up here earlier when I couldn't figure out how to advance the DK starting quest line. If you go to the mailbox and zoom your camera in a bit, you will notice a note/scroll thing. Click on THAT, and NOT the mailbox, and you can advance the quest! Hope this helps someone!