"Unsafe environments" refers to the use of those systems which the user either shares with other ones or have no administration privileges.
1. Because the settings for the current mailbox group is saved into the hard disk of the system when the program exits normally, it can not be carried away by the user. It is suggested to setup an empty mailbox group and save it to a configuration file. When the user needs to exit inside a unsafe environment, he/she should load the empty mailbox group first before hitting the exit button. There will be no private information left on the system after exiting using this step. Since there is no setting file, it wouldn't be useful for other's even if he/she knows your master passphrase.
2. E-mail storage directory should be located on a user's own mobile disk.