No, why should the authentication determine how the user names look 
like? Anyway, if your system to allows logging in both, with and 
without the domain part of the username, Horde will break. Use a hook 
to normalize your user names when logging in.

Interestingly, I remember that this does not happen when logging in 
via the web interface with short names ("joe.user"). All calendars are 
correctly shown. Of course, the described behaviour only makes sense 
when using IMP login I think (otherwise, you won't be able to log in 
via the email address at all, right?).

The RPC server uses the same authentication method like other parts of 
Horde, so this should happen with the main interface too.

When using XML/RPC to interface with Horde, one must give the full 
email address of the user to authenticate.



However, when one accidentially only gives the login name (say, 
"joe.user" instead of "joe.user@my-server.com"), authentication still 
succeeds but behaviour is incosistent. E.g., in the example 
http://wiki.horde.org/XmlRpcPythonHowTo an incorrect list of calendars 
is returned and retrieving any calendar fails with an "access denied" 
message.



To resolve this, either specifying only the login name should fail 
completely or the behaviour of both login methods should be consistent.