V8 sendmail, if compiled with USERDB defined
(USERDB), can use a special, internally
understood database called the User Database. Addresses that are
defined in the User Database can be looked up and modified after
aliasing but before the processing of the user's
The workings of this database are described in userdb. The UserDatabaseSpec
option defines the name and location of the file containing this User
The forms of the UserDatabaseSpec option are as
O UserDatabaseSpec=path,... configuration file (V8.7 and later)
-OUserDatabaseSpec=path,... command line (V8.7 and later)
define(`confUSERDB_SPEC',``path,...'') mc configuration (V8.7 and later)
OUpath,... configuration file (deprecated)
-oUpath,... command line (deprecated)
The argument path, . . . is of type
string and is a comma- or space-separated list of
elements. Those elements can be database pathnames, or other
information as described next. If path, .
. . is missing or if the entire option is missing, the User Database
is not used. Otherwise, the User Database is used, and each database
is accessed in turn, leftmost to rightmost, in the list of paths.
There is no default for the mc technique.
The elements of path, . . . can either be
pathnames of files or other methods of lookup, depending on the first
character of each:
A lead slash causes the element to be interpreted as a pathname; for
A leading @ causes a copy of the message for each
user to be forwarded to a specified host. The assumption is that the
other host is in a better position to perform user database lookups.
Such a declaration looks like
@dbhost.our.domain. Note that this form of
declaration must be last in the list that constitutes
path, . . . because it always succeeds.
Beginning with V8.7, a leading h or
H causes sendmail to perform
a case-insensitive comparison of the path
to the string hesiod. If they match, user database
inquiries are looked up via Hesiod services.
For example, the following declares two user databases. The
/etc/mail/userdb database is used first. If the
entry is not found in that database, it will be forwarded to the host
mail.here.us for handling there:
Any leading character other than those shown here causes an error
message to be printed and that particular
path, . . . element to be ignored:
Unknown UDB spec badpath
If UDB_DEFAULT_SPEC is defined when sendmail is
compiled (UDB_DEFAULT_SPEC), that value becomes the
default if the UserDatabaseSpec option is missing.
If UDB_DEFAULT_SPEC is undefined, the default becomes NULL and no
User Database lookups are performed.
The UserDatabaseSpec option is not safe. If
specified from the command line, it can cause
sendmail to relinquish its special privileges.