nPOPuk is a tiny comprehensive portable email client for Windows-based operating systems.

POPuk differs from many other email programs; for a start, it is a true client/server application. Each nPOPuk account will communicate directly with a POP3 and SMTP server and only record what is present on those servers. The implications of this are explained below.

Being a client/server application means mail is read directly from the server and, initially, held only in memory rather than saved to disk before being displayed. This fact means that if mail is deleted from the server by another program the next time nPOPuk connects to the server that mail will also disappear from the "Account" in nPOPuk, and will be permanently lost. This is true even if you have the default option set to save mail found on the server, as an nPOPuk account is only a record of mail located on the server at the time of the last connection with the server.

Most mail programs hide all server communication from the user. They save all mail within the program on the host computer deleting it from the server as it is downloaded. In nPOPuk, this would be called "transferring" the mail (by a move or copy) to a "Savebox," and furthermore, this can be done automatically using mail filters, so the net result is the same as a conventional program. The ability to distinguish between mail found on the server (shown in an nPOPuk "Account") and that held locally (in an nPOPuk "Savebox") makes it ideal for the more Specialist Tasks that don't require off-line copies of mail and this is what gives nPOPuk its edge over many other email programs.