To disable multiple identities in Roundcube you need to edit the following file: config/main.inc.php
and in it locate this section:
// Set identities access level:
// 0 - many identities with possibility to edit all params
// 1 - many identities with possibility to edit all params but not email address
// 2 - one identity with possibility to edit all params
// 3 - one identity with possibility to edit all params but not email address
$rcmail_config['identities_level'] = 3;Setting the value of identities_level to 3 disables users to change the from email address.
