Better Outbox adds the following 2 features to the outbox frame: Autocompletion of your alts automatically. Helps when you have non-guilded alts, Autofills the subject if no subject is set and you are only sending money, Autofills the recipient with the last person mailed.
Adds a several mailing options to your mail window. Mass Mailing: This option allows you to send up to 21 items or stacks of items to the same person with one click. Simply enter their name and add the items, the subject will automatically show each items name. The total amount for sending all mails will be calculated into the upper right of the window, and an optional confirmation box will ensure you know. Each mail will start to send when the previous mail has sent. Adds the ability to Alt+Click item functionality. Alt+clicking an item will add it to both regular mail and Mass Mail screens, as well as to a trade window with another player. A Forward button has been added when reading a mail, which will pull any item out of a mail, put it into your inventory, attach it to a new mail, and send to the specified recipient. In addition to the sending tools, CT_MailMod also adds tools for receiving mail. Adding checkboxes to the left of each message, you can check the ones you would like to open, and hit Open Selected at the top to 'mass-open'. Or if you would like to open all of your mail at once, hit the Open All key. Note that when Open All is pressed, any mail with messages only (no items or coin) will be skipped. Additionally items that are unique will be skipped.
MailNotifier is a small addon that has two purposes: tracking how many unread mails the player has in the inbox and alerting him when new mail is received (plays a sound and flashes the minimap mail button).
Picks up all items and gold from your inbox.
Mail mod that allows quick bulk mailing by filling in the recipient name in the mail frame then alt-clicking items in your bags to send the item. Shift click mail items to collect them directly into your bags. Also allows the user to open all items, or return checked items.
Review: WoW Insider
This addon will increase the functionality of Blizzards built in player name auto-complete for the Mail Window. It will also add a button to 'Open All' items from your mailbox with a single click. This addon will give you an 'Open All' button on the top of the inbox window to retrieve all your mail with a single click.