AOL Instant Messenger

Being the second modern client after ICQ, AIM was initially released in 1997.

AIM servers filter strings containing <img and <script, which are tags in the Hypertext Markup Language (HTML) AIM uses to encode messages (so as to support fonts, colors, etc.).

HTML tags that you put into the inputline are “escaped” by Adium, so that the recipient's client will not attempt to use the HTML tag; it will simply display the text of the tag. However, it appears that the AIM server drops messages containing even escaped HTML (but only those two tags—other tags work fine).

AIM will also drop any message containing a link to a file: address. These addresses are intended to refer to files on the sender's or your computer. (The file need not actually exist on one end or the other. A perfectly valid file: link can refer to a path that does not exist on anyone's machine, such as this one.)

On the other hand, it will allow the message if the address is plain text instead of a link. So, for example, “Check out what I just wrote: file:///Users/me/Documents/Why-Adium-is-awesome.txt” will go through, but “Check out what I just wrote” will not.