[imp] So confused with type of hooks

[Manuel Mely]

Hi,

I'm still trying to make own hook, but i'm a little confused about what 
hook function to use. Can somebody explain me which of this functions i 
should use in order to change my auth to pop3 server as user at domain:

- _username_hook_frombackend
- _username_hook_tobackend
- _horde_hook_preauthenticate
- _imp_hook_vinfo

I'm not using Horde Authentication, just IMP.

Greetings.
M