The following information is valid for SeaMonkey 1.x only.
Assuming that mozilla/ is the directory where the SeaMonkey executable resides, Enigmail creates the following files as a result of its installation:
mozilla/components/enigmail.js
enigmail.xpt
libenigmime.so on Linux, enigmime.dll on Windows
enigmime.xpt
ipc.xpt
enigprefs-service.js
mozilla/chrome/enigmail.jar
These are the files to delete if, for any reason, you want to do a manual uninstall.
Enigmail also modifies the following two overlay files by inserting Enigmail-
related lines:
mozilla/chrome/overlayinfo/communicator/content/overlays.rdf
mozilla/chrome/overlayinfo/messenger/content/overlays.rdf
Do not manually delete mozilla/chrome/enigmail.jar without removing the Enigmail entries from the overlays.rdf files; this could cause SeaMonkey to hang.