Configuration/settings/login append domain if missing
From DAViCal Wiki
If email addresses are used as user names in Davical, the MacOS X 10.6 Addressbook cannot login to CardDav account. This problem is caused by a bug in Addressbook URL parsing and cannot be fixed on the client side. To allow "user@domainname" users to login as "user" this options solves the problem on server side.
$c->login_append_domain_if_missing
If this option is set to 1, then the "@$c->domain_name" is appended to user login if it not contains @ character.
Available from DAViCal version: 0.9.8.5 and later

