Direct Client-to-Client (DCC) is an extension of the IRC protocol that enables the ability to transfer files between users using a direct connection between each user instead of sending data through the IRC server itself.
This page will stand as the official response as to whether the Textual IRC Client supports DCC file transfers:
It is the official stance of the Textual IRC Client project to NOT support file transfers through DCC.
This stance has been taken because we believe there are much better services available to handle file transfers. The move to not support DCC file transfers is an effort to phase it out of the IRC community in favor of these faster, more secure alternatives.
Many great changes have happened to the Internet since the time that DCC was conceived. One of the greatest changes to occur is the is availability of easy-to-use & secure file sharing services. There are now hundreds of file sharing websites, better protocols such as BitTorrent, and cloud based services such as CloudApp and Dropbox.
It is recommended to research these alternatives.