UnlimitedChatMessage 

Check UnlimitedChatMessage on Curse.com for the latest version.

UnlimitedChatMessage (UCM) removes the 255 character limit from the chat editbox allowing you to send extra long messages into chat. It does this by breaking up your outgoing message into smaller 255 character messages.

Ever try to post a dungeon walk threw into chat but can't paste the whole text into the edit box? UCM solves that problem.

With multi-line support enabled, each line will be sent as it's own message.
Known issue:
Message history (up arrow) breaks with multi-line enabled. I recommend keeping it disabled and using /ml to temporarily allow multi-line messages.

RealID users:
UCM does not support unlimited length realID messages. When typing a message for realID the chatbox will return to default max character limit (255).

Donations welcome. There's a donate button on here.
Bitcoin address: 12Z1ExLqeSNrrmRUW82jbt3eNjcKsaLwty