Items or gold left in the mailbox for too long is deleted
To gift an item, click Gift instead of Buy Now on the item’s page.
How to resolve an Internal Mail Error when looting mail.
How and when BoA or Heirloom items be sent to another character on the Blizzard Account.
More information on returned mail
Information on how long it may take for different kinds of mail to be delivered.
Troubleshooting steps for missing Auction House mail reports
Troubleshooting World of Warcraft in-game mail issues.
Gold and items cannot be sent to another realm or faction.
Troubleshooting mail sent without adding a CoD.