Several conf file settings apply directly to bans. This exerpt comes from /eggdrop/doc/BANS:
Global modes These modes will be active on every channel the bot monitors. Some will "expire" after a while (be removed automatically). Others are considered "permanent" and can only be removed by a master.
Channel modes These modes are active only on one channel, and are almost always temporary modes that expire after an hour or so (depending on how long you've specified in the config file). Usually they're created by a Tcl script of some sort.
Non-bot modes These are modes that were not placed by the bot. They can be removed by anyone on the channel. The other two types of modes are protected by the bot (unless the channel settings specify otherwise), and have to be removed via the bot.
Mode behavior:
Bans If the channel is supporting dynamic bans, then the ban is set when a user with a matching hostmask joins the channel; otherwise, the modes are permanently set. On a channel with dynamic bans, the ban expires after 'ban-time' minutes (which is specified in the config file).
Hope this helped.
