Pam_dotfile is a pam module which allows users to have more than one password for a single account, each for a different service. this makes sense since many users have objections to use the same password for (as an example) the imap4 mailbox and the ssh access. the imap4 password should be distinct from the ssh password since the user wants to save the former in the configuration of his mail agent, but not the latter. the same applies to pop3 mailboxes, ftp and comparable services.