We introduce a seamless messaging system for the management of personal messages. The aim of it is to intercept, filter, interpret, and deliver multi-modal messages (voice, fax, and/or e-mail messages). Messages are delivered to the recipient regardless of their target messaging device. Seamless messaging involves finding the person (if urgent) and delivering the information to them on their cellular phone, pager, laptop, nearest fax, telephone, or desktop computer. The system includes a set of personal agents that classify and act on incoming messages based on their content. The user specifies the classes and actions to the agent as a set of high-level rules. This allows the user to specify rules that are independent of the messaging system and target devices. A personal agent "Secretary" is responsible for mediating between the different messaging environments, the target devices, and other interacting applications (e.g., calendars, e-mail programs, etc.). The design of this Seamless Messaging System is based on the integration of three technologies, ubiquitous computing, information filtering, and telematics. The system has been implemented on a Lotus Notes platform. What makes the system unique is its approach to treating a message in a universal manner, its ability to mediate between different messaging devices, and its ability to try to determine the availability of the user.