Session can send files, images and other attachments up to 6MB in both person-to-person conversations and group chats. This file size limit will increase in future versions of Session.
By default, Session uses the Oxen File Server for attachment sending and storage. The Oxen File Server is an open-source file server run by the Oxen Privacy Tech Foundation — the creators of Session. When you send an attachment, the file is symmetrically encrypted on the device and then sent to the Oxen File Server. To send the attachment to a friend, Session sends them an encrypted message containing the link, plus the decryption key for the file. This ensures that the Oxen File Server can never see the contents of files being uploaded to it.