Sendmail Installation and Operation Guide
SMM:08-37
4.12. Moving the Per-User Forward Files
Some sites mount each user's home directory from a local disk on their workstation, so that
local access is fast. However, the result is that .forward file lookups from a central mail server are
slow. In some cases, mail can even be delivered on machines inappropriately because of a file
server being down. The performance can be especially bad if you run the automounter.
The ForwardPath (J) option allows you to set a path of forward files. For example, the con-
fig file line
O ForwardPath=/var/forward/$u:$z/.forward.$w
would first look for a file with the same name as the user's login in /var/forward; if that is not found
(or is inaccessible) the file ``.forward.machinename'' in the user's home directory is searched. A
truly perverse site could also search by sender by using $r, $s, or $f.
If you create a directory such as /var/forward, it should be mode 1777 (that is, the sticky bit
should be set). Users should create the files mode 0644. Note that you must use the ForwardFileIn-
UnsafeDirPath and ForwardFileInUnsafeDirPathSafe flags with the DontBlameSendmail option to
allow forward files in a world writable directory. This might also be used as a denial of service
attack (users could create forward files for other users); a better approach might be to create
/var/forward mode 0755 and create empty files for each user, owned by that user, mode 0644. If
you do this, you don't hav e to set the DontBlameSendmail options indicated above.
4.13. Free Space
On systems that have one of the system calls in the statfs(2) family (including statvfs and
ustat), you can specify a minimum number of free blocks on the queue filesystem using the Min-
FreeBlocks
(b) option. If there are fewer than the indicated number of blocks free on the filesystem
on which the queue is mounted the SMTP server will reject mail with the 452 error code. This
invites the SMTP client to try again later.
Beware of setting this option too high; it can cause rejection of email when that mail would
be processed without difficulty.
4.14. Maximum Message Size
To avoid overflowing your system with a large message, the MaxMessageSize option can be
set to set an absolute limit on the size of any one message. This will be advertised in the ESMTP
dialogue and checked during message collection.
4.15. Privacy Flags
The PrivacyOptions (p) option allows you to set certain ``privacy'' flags. Actually, many of
them don't giv e you any extra privacy, rather just insisting that client SMTP servers use the HELO
command before using certain commands or adding extra headers to indicate possible spoof
attempts.
The option takes a series of flag names; the final privacy is the inclusive or of those flags. For
example:
O PrivacyOptions=needmailhelo, noexpn
insists that the HELO or EHLO command be used before a MAIL command is accepted and dis-
ables the EXPN command.
The flags are detailed in section 5.6.
4.16. Send to Me Too
Beginning with version 8.10, sendmail includes by default the (envelope) sender in any list
expansions. For example, if "matt" sends to a list that contains "matt" as one of the members he