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11-15-2010 01:32 AM
11-15-2010 01:32 AM
The sendmail daemon in my node (redhat 5.3 64-bit) is configured to use a relay server (other node), i.e., any e-mail message sent (to a non-local recipient) from my node is re-sent to the relay node in order to be successfully delivered --- This behaviour is the required...
my problem is that I cannot find the sendmail config file where this feature is found, i.e., the DS directive in the /etc/mail/sendmail.cf is empty...
Are there other files where relay may be configured?
Thanx in advance
Solved! Go to Solution.
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11-15-2010 07:43 AM
11-15-2010 07:43 AM
SolutionIt might be configured using /etc/mail/mailertable. (If it's done this way, then the previous admin probably did not know about the DS setting of sendmail.)
Or your server might have iptables redirection rules to force all outgoing connections to port TCP/25 to the relay server.
Run:
iptables -L -v -t nat
If you see rules with target "DNAT" and destination is something like "anywhere tcp dpt:smtp --to-destination
The cause might even be external to your server: your site's DNS server might be configured to respond to all requests for remote domains' MX records with the address of the relay server.
Test using "dig" and the domain name of a non-local email recipient. For example, if the recipient was "someone@nonlocal.com.example", you might run:
dig nonlocal.com.example mx
If this returns records pointing to your relay node, then the DNS server is causing the redirection.
Another way to enforce such a redirection externally would be to use transparent proxying technology in your site's outgoing router.
MK
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11-15-2010 12:16 PM
11-15-2010 12:16 PM
Re: sendmail configured to use a relay node
Use 'alternatives --display mta' to confirm that sendmail is the configured MTA.
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11-15-2010 10:54 PM
11-15-2010 10:54 PM
Re: sendmail configured to use a relay node
# ll /etc/mail/mailertable
-rw-r--r-- 1 root root 0 Nov 28 2006 /etc/mail/mailertable
# iptables -L -v -t nat
Chain PREROUTING (policy ACCEPT 29952 packets, 4128K bytes)
pkts bytes target prot opt in out source destination
Chain POSTROUTING (policy ACCEPT 1022 packets, 88837 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 1022 packets, 88837 bytes)
pkts bytes target prot opt in out source destination
# dig nonlocal.com.example mx
; <<>> DiG 9.3.4-P1 <<>> nonlocal.com.example mx
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 63476
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;nonlocal.com.example. IN MX
;; AUTHORITY SECTION:
. 10800 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2010111500 1800 900 604800 86400
;; Query time: 32 msec
;; SERVER: 10.9.236.7#53(10.9.236.7)
;; WHEN: Tue Nov 16 07:51:07 2010
;; MSG SIZE rcvd: 113
# alternatives --display mta
mta - status is auto.
link currently points to /usr/sbin/sendmail.sendmail
/usr/sbin/sendmail.sendmail - priority 90
slave mta-mailq: /usr/bin/mailq.sendmail
slave mta-newaliases: /usr/bin/newaliases.sendmail
slave mta-rmail: /usr/bin/rmail.sendmail
slave mta-sendmail: /usr/lib/sendmail.sendmail
slave mta-pam: /etc/pam.d/smtp.sendmail
slave mta-sendmailman: /usr/share/man/man8/sendmail.sendmail.8.gz
slave mta-mailqman: /usr/share/man/man1/mailq.sendmail.1.gz
slave mta-newaliasesman: /usr/share/man/man1/newaliases.sendmail.1.gz
slave mta-aliasesman: /usr/share/man/man5/aliases.sendmail.5.gz
Current `best' version is /usr/sbin/sendmail.sendmail.
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11-16-2010 04:16 AM
11-16-2010 04:16 AM
Re: sendmail configured to use a relay node
Double check the virtusertable (makemap -u hash /etc/mail/virtusertable.db), see if that has any mappings.
If that doesn't show anything, then you're down to manual runnings of sendmail with high levels of logging or debugging to find out where it's coming from :(
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11-16-2010 04:31 AM
11-16-2010 04:31 AM
Re: sendmail configured to use a relay node
My DNS provides a MX record:
mydomain.com mail exchanger = 10 myrelay.mydomain.com.
Thank everyone
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