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Recently took over a seemingly undocumented Sendmail 8.13.1 server, running on CentOS 4.7.

Basically need to figure out what they are trying to accomplish via the config files. One thing that I find odd is that many domains appear in both the relay-domains file as well as the local-host-names file. What might be the reason for such a configuration?

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It may make some sense without FEATURE(relay_hosts_only).

local-host-names file ($=w) does not automatically catch subdomains of the listed names.
relay-domains file ($=R) *without FEATURE(relay_hosts_only)*automatically catches also sub-domains.

Exact domains with names listed in both files will be treated as listed in local-host-names but their sub-domains will be treated as listed in relay-domains.

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It appears that FEATURE(relay_hosts_only) is not being used. It's not listed in the and contains "$* $=R" entries as opposed to "$=R" entries. But I don't get what you're saying - what would be the effect of the same entry in both files (outside of confusion)? It seems that it may make a difference with FEATURE(relay_hosts_only) as then the subdomains might get locally delivered instead of relayed but I'm not even sure that would happen. – user168261 May 22 '13 at 1:12
IF is present in both files THEN* is treated as listed in local-host-names (it is a local email domain) AND is treated as listed in relay-domains ( sendmail will relay from and to it) FI. – Andrzej A. Filip May 22 '13 at 6:44

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