They are also not compatible with the digest version of the mailing lists. If you have a file which you wish to share with others on the list, either upload it to a web site and then send the URL to the list together with a description of the file, or advertise the availability of the file to the list and then e-mail it directly to any interested parties. Most likely you posted your message in HTML format, or included a file attachment. A third common reason is that you posted your message from an e-mail address that the mailing list doesn't recognise. If this happens you will receive an email explaining the likely cause of the problem.
Some Internet users rely on abbreviations to save a bit of typing.
These are little faces, sideways on, made from the characters you can find on your keyboard. As the method for changing this setting depends on which software you are using, we are not able to give details on how to change it here. You should consult your e-mail software's online help facility for further details.