https://www.wowace.com/projects/bulkmail?comment=172

Found how to send Armor > cosmetics to alts, but there is no Weapon cosmetic option. Would like that if possible. Still haven't found a way to send BoE items for disenchant when they are not cosmetic for another alt.

Not been playing retail, didn't even know these were a thing..

This is based on Auction House categories and apparently there's no category for cosmetic weapons - they show up in the same category as the weapon. So the way to do it is simply to mail all weapons - all weapons are really cosmetic if you think about it. not optimal but that's how it works sadly.