Note that eMule may save its configuration files in C:\ProgramData\eMule\config (this is the option “for all users”), instead of inside its own folder. You can change this at advanced settings > extended. eMule System Files:

Known.met: It saves all files which eMule knows for if they are shared, files currently in the download list or downloaded in the past. Information like file size, filename, hash sets, hash values and some statistics is saved for each and every file. If you delete this, eMule will have to rehash all files on the next restart.

Known2_64.met: Stores AICH hashes of all downloaded and / or shared files. If you delete this, eMule will have to rehash all files on the next restart.

Cancelled.met: All files which you cancelled before completing their download are noted here, so eMule can mark them to let you avoid redownloading them again.

Clients.met: It stores all users who have credits with your eMule.

Server.met: It contains all the known servers.

Emfriends.met: If users are added as your friends, they are stored in this file.

Preferences.ini: It saves all preferences that you set in the Options dialog, as well as information about visual details (column size etc). Some development related and advanced options can only be enabled by editing this file directly with a text editor.