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Even though this article is from 1985, it describes the rewriting process of sendmail pretty well.
cf/READMEfile from the sendmail distribution explains how to build a configuration file for your specific needs from a simple m4 description file.
Other questions should be answered in the FAQ for sendmail.
* I'm getting "Local configuration error" messages, such as:
553 MX list for domain.net points back to relay.domain.net 554 <email@example.com>... Local configuration error How can I solve this problem? You have asked mail to the domain (e.g., domain.net) to be forwarded to a specific host (in this case, relay.domain.net) by using an MX record, but the relay machine doesn't recognize itself as domain.net. Add domain.net to /etc/sendmail.cw (if you are using FEATURE(use_cw_file)) or add "Cw domain.net" to your configuration file. IMPORTANT: When making changes to your configuration file, be sure you kill and restart the sendmail daemon (for ANY change in the configuration, not just this one): kill `head -1 /etc/sendmail.pid` sh -c "`tail -1 /etc/sendmail.pid`" NOTA BENE: kill -1 does not work with versions prior to 8.7.y!
How can I solve this problem? There are two possibilities:
dom.ain) to be forwarded to a specific host (in this case,
relay.dom.ain) by using an MX record, but the relay machine doesn't recognize itself as
/etc/sendmail.cw(if you are using
FEATURE(use_cw_file)) or add
Cwdom.ainto your configuration file.
relay.dom.ainshould send this to another host
mail.dom.ainwhich really handles the mail for
dom.ain. If this host is reachable by SMTP you should create an MX record with the best (lowest) priority pointing to
mail.dom.ain. Make sure that
relay.dom.ainreally knows it is
relay.dom.ain! If you setup the MX records, you must use the correct name for
mail.dom.ainis reachable by some other mail transport protocol (UUCP) or it is not directly reachable from the outside, you may have a look at the feature mailertable. E.g., use in your .mc configuration file something like
FEATURE(mailertable,`dbm -o /etc/mailertable')(or another database type, see
makemap(8)) and add a line like the following to the mailertable:
dom.ain smtp:[mail.dom.ain]The square brackets (
[ ]) tell sendmail to ignore MX records for
Two more hints:
An MX record shouldn't point to a CNAME, it will most probably cause
you a lot of trouble.
(And currently it violates
And from src/READ_ME:
WILDCARD MX RECORDS ARE A BAD IDEA! The only situation in which they work reliably is if you have two versions of DNS, one in the real world which has a wildcard pointing to your firewall, and a completely different version of the database internally that does not include wildcard MX records that match your domain. ANYTHING ELSE WILL GIVE YOU HEADACHES!
IMPORTANT: Be sure you kill and restart the sendmail daemon after you change the configuration file (for ANY change in the configuration, not just this one):
kill `head -1 /etc/sendmail.pid` sh -c "`tail -1 /etc/sendmail.pid`"
NOTA BENE: kill -1 does not work!
See also next paragraph for a related question!
If it still doesn't work, take a look at some more explanations.
* How do I make all my addresses appear to be from a single host?
Using the V8 configuration macros, use:
This will cause all addresses to be sent out as being from
the indicated domain.
If you're using version 8.7 sendmail, and you want to hide this information in the envelope as well as the headers, use:
If you also want to masquerade the recipients, use
FEATURE(allmasquerade)But be careful and read cf/README about possible problems!
Another section in cf/README explains how to masquerade for other hosts too. Usually, masquerading works only for all elements of class w. This class contains all names local to that host. But you can also add more hosts to class M which will be masqueraded too.
sendmail 8.8 offers even more flexibility with respect to masquerading.
You may also have a look at the genericstable FEATURE.
sendmail 8.8 has some new rulesets to check who can use your machine as a mail gateway. Using check_* in sendmail 8.8 gives an overview how to use these rulesets, 8.9 has standard FEATUREs to this effect.
If you have sendmail 8.x (with x < 8), then you should upgrade.
Another possibility is to use tcp_wrappers, so you can define the access to your sendmail daemon based on the rules available for tcp_wrappers .
sendmail 8.8 and later support this directly, just use
for compilation and add the appropriate library
There is a patch for a problem with
which passes incorrect data to the library routines.
A patch can be found in
for pointing this out.
A third possibility is to use the
proposed the following
It is intended to disallow all non-local e-mail traffic through your host.
Use at your own risk.
unsafe map file /etc/mail/aliases(or another map). There may be several reasons for this, the most common is that the permissions of the directories leading to the alias file are incorrect. It must be:
drwxr-xr-x 12 root staff 3072 Nov 20 10:47 /etc/ drwxr-xr-x 4 root staff 1024 Dec 21 16:40 /etc/mail/i.e., the directory must be owned by root and not writable by the group or the rest of the world. The alias file itself must have similar permissions. Moreover, if you have a db map, you may try to touch the resulting map (file.db) and call makemap or newaliases thereafter.
See the release notes for further details. /usr/lib/sendmail -bi -d44.4 gives some debug output for the alias map.