Analysis of information sources in references of the Wikipedia article "Cybersex" in English language version.
The goal of mud sex is the same as the goal of regular sex (without the babies): to bond temporarily in a way that is physically and emotionally satisfying. To do so, two people will exchange messages so as to lead one another into a high level of sexual arousal, culminating in a well-defined resolution.
To be blunt, most mud sex is also accompanied by the people sexually gratifying themselves in real life at the same time.
MUD SEX refers to the acting out of erotic feelings by two people while typing a series of sexually explicit messages. (Mud sex is also referred to as NET SEX or—on a TinyMud—TINYSEX.)
Finally, don't forget that the characters on a mud will not correspond exactly to the people in real life. In particular, what looks like a woman may really be a man. HINT: If you are a guy, and you go up to a female character on a mud and say, "Hi, wanna have sex?", and she says yes right away, chances are she is another guy playing a female role.