ubuntu couldn t find package courier-authlib-mysql

This is a known issue...
in fact, this error is not important...

ehcp try to install both courier auth libraries, whichever available for your current system.

only one of them installable,
thats why, one of them fails to install, which is normal.

this is done to guarantee install of one of courier auth libraries.
the names are different, so, both is tried to install.

dont wory about this error..
your ehcp installation should work okey ...

see you.