Hello!

auth_pam  - в аттаче. Это про исходники. Там совсем немного. А вот ответ
pam на добавление параметра debug во все три строчки /etc/pam.d/openwebmail:

Mar 12 22:44:00 peet pam_stack[6515]: called for "PAM_AUTHENTICATE"
Mar 12 22:44:00 peet pam_stack[6515]: called from "openwebmail"
Mar 12 22:44:00 peet pam_stack[6515]: initializing
Mar 12 22:44:00 peet pam_stack[6515]: creating child stack `system-auth'
Mar 12 22:44:00 peet pam_stack[6515]: creating environment
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_AUTHTOK to child: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: passing PAM_CONV to child
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_FAIL_DELAY to child: source not set
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_OLDAUTHTOK to child: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_RHOST to child: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_RUSER to child: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: passing PAM_SERVICE to child
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_TTY to child: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: passing PAM_USER to child
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_USER_PROMPT to child: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: passing data to child
Mar 12 22:44:00 peet pam_stack[6515]: calling substack
Mar 12 22:44:00 peet pam_tcb[6518]: Credentials for user nata unknown
Mar 12 22:44:00 peet pam_tcb[6515]: openwebmail: Authentication failed for UNKNOWN USER from (uid=96)
Mar 12 22:44:00 peet pam_stack[6515]: substack returned 9 (Authentication service cannot retrieve authentication info.)
Mar 12 22:44:00 peet pam_stack[6515]: passing PAM_AUTHTOK to parent
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_CONV to parent: destination already set
Mar 12 22:44:00 peet pam_stack[6515]: passing PAM_FAIL_DELAY to parent
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_OLDAUTHTOK to parent: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_RHOST to parent: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_RUSER to parent: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: passing PAM_SERVICE to parent
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_TTY to parent: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: passing PAM_USER to parent
Mar 12 22:44:00 peet pam_stack[6515]: NOT passing PAM_USER_PROMPT to parent: source is NULL
Mar 12 22:44:00 peet pam_stack[6515]: passing data back
Mar 12 22:44:00 peet pam_stack[6515]: passing former back
Mar 12 22:44:00 peet pam_stack[6515]: returning 9 (Authentication service cannot retrieve authentication info.)
Mar 12 22:44:02 peet pam_stack[6515]: freeing stack data for `system-auth' service

Петр.