I set it up so that the default is that you CAN send to the other faction, etc. Check your mangosd.conf file to make sure it's set like the following:
You can also change how long the delay is for sending items in the mailCode:AllowTwoSide.Accounts = 1
AllowTwoSide.Interaction.Chat = 1
AllowTwoSide.Interaction.Channel = 1
AllowTwoSide.Interaction.Group = 1
AllowTwoSide.Interaction.Guild = 1
AllowTwoSide.Interaction.Auction = 1
AllowTwoSide.Interaction.Mail = 1
AllowTwoSide.WhoList = 1
AllowTwoSide.AddFriend = 1
TalentsInspecting = 1
That's the default (1 hour), set it to whatever you'd like.Code:MailDeliveryDelay = 3600
Give me a few minutes I'll check the Dalaran Sunreaver vendor.
EDIT: Ok, I tested Magister Arlan <Emblem of Frost Quartermaster> in Dalaran and I cannot replicate your problem:
http://www.youtube.com/watch?v=780dPOAinus
I would suggest 1 of 2 things:
1. Go into your World of Warcraft/Cache folder and delete everything there then restart
2. Run World of Warcraft - Repair