Mail addresses on JANET use what is known as notation, with the top level domain given first. The rest of the world uses "little endian" notation, with the bottom domain given first. For example:
Although many people in the UK academic community still give their addresses in JANET notation, it is better to give it in the notation used (and understood) by the rest of the world.
Your mail program might be configured to handle mail adresses given in either notation. Check with your system administrator for further information.