dbm and ndbm forms of the
aliases(5) database files contain binary
integers. As a consequence, those database files cannot be shared via
network-mounted filesystems by machines of differing architectures.
This is not a problem for Sleepycat db files.
The aliases file and database files can be used
to circumvent system security if they are writable by the wrong
users. Proper ownership and permissions are checked and enforced only
by V8.9 and above sendmail. Restrictions on who
can rebuild are enforced beginning with V8.11
Versions of sendmail that use the old-style
dbm(3) libraries can cause overly long alias
lines (greater than 1024 bytes) to be silently truncated. With the
new databases, such as ndbm(3), a warning is
printed. Note that V8 sendmail does not support
old-style dbm(3) for this very reason.
Recursive (circular self-referencing) aliases are detected only when
mail is being delivered. The sendmail program
does not look for such alias loops when rebuilding its database.
Because of the way V8.8 sendmail and above lock
the alias file for rebuilding on some operating systems, that file
must be writable by root. If it is not,
sendmail prints the following and skips the
warning: cannot lock aliases: Permission denied
This can be a problem if the master alias file is shared via NFS
because root is normally mapped to